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Materials and devices for energy and environment applications


Transparent conducting and semiconducting oxides and their applications

Introduction and scope:

The goal of the proposed symposium is bring together an international audience to contribute, learn and discuss about the latest developments in the topical research field of transparent conducting oxides (TCO) and transparent semiconducting oxides (TSO). Concerning TCOs, the focus is laid on Indium-free materials and their applications. Concerning TSOs, the focus is on novel semiconducting oxides such as n-type materials like group-III sesquioxides and on p-type semiconducting oxides such as NiO or the copper-based delafossites CuMO2 (M=Al, Ga, In, Y,Sc, La…) and first demonstrator devices.

Indium tin oxide is widely used in making transparent thin film coatings for several technological areas, including heat-retaining window glass and electrodes for components that interact with light. These include flat panel displays, flexible electronics, photovoltaic cells and LEDs, both inorganic and organic. However, the cost and narrowness of supply of Indium pose a perceived threat to the global electronics, having led to growing international research and development of Indium-free replacement materials, and their deposition technologies.

Generically, these replacement materials are transparent conducting oxides (TCOs) that behave as wide band-gap semiconductors, but their application as transparent contact materials gives rise to the conflicting requirements of high electrical conductivity and transparency. Further, electrical conductivity depends on more fundamental semiconductor properties like carrier mobility and doping efficiency. In optoelectronic applications, heterojunction formation with the active device structure introduces further complexity in developing optimum p-type and n-type TCO technologies.

Aiming to meet these requirements, has created a global research area, not widely served by specialist symposia, that address the following scientific and technical issues:

  • Fundamental transport properties of Indium-free TCOs
  • Electrical and optical performance of In-free TCOs and their characterisation
  • Deposition technologies and precursor development for TCOs
  • Applications of In-free TCOs to organic and inorganic light emitting devices
  • Solar-cell applications of In-free TCOs
  • In-free TCOs for touch-screen technologies

Fully transparent electronic devices demand besides transparent electrodes also an active layer being transparent. Metal oxides can form such layers as well. Control of doping and stoichiometry leads to transparent semiconducting oxides. Besides the possibility to create a transparent logic such materials find also potential application as gas sensors, visible-blind or solar-blind photodetectors, and rectifiers and transistors for high power electronics. The large band-offset that can be realized in heterostructures of semiconducting oxides results in high confinement energies of two-dimensional carrier gases allowing realization of HEMT structures or QWIPs. The combination of n-type and p-type semiconducting oxides results in type-II or type-III heterodiodes being of fundamental research interest, especially for the latter case.

Hot topics to be covered by the symposium

  • Precursor development for TSOs/TCOs
  • Bulk and thin film growth of TCOs/TSOs
  • Alloying and doping of TSOs
  • Electronic structure and transport properties of TCOs/TSOs
  • Applications of (In-free) TCOs to inorganic light emitting devices
  • Applications of (In-free) TCOs to organic semiconductor devices
  • Solar-cell applications of (In-free) TCOs
  • UV TCOs
  • Oxiced for electrochemical applications including water splitting
  • Unipolar devices
  • Bipolar devices
  • Fully transparent devices by combining TSOs and (Indium-free) TCOs

List of invited speakers:

  • Man Hoi Wong, National Institute of Information and Communications Technology Japan: “Engineering Ga2O3 for high-voltage MOSFETs: transport properties, electrical characterization, and thermal analysis”
  • Zbigniew Galazka, IKZ, Germany: “Bulk single crystals and properties of transparent semiconducting oxides”
  • Geoffroy Hautier, Université Catholique de Louvain, Belgium: “Accelerating the discovery of high mobility transparent (semi)conducting oxides through high-throughput computing”
  • James Dutson, Plasma Quest Ltd, United Kingdom: “Advances in Sputter Deposition Technologies for Large Area, Thin Film Transparent Conducting Oxide Coatings”
  • David Cherns, University of Bristol, United Kingdom: “Transmission electron microscopy of ZnO, TiO2 and InGaN nanorod arrays for solar cell applications”
  • Mariadriana Creatore, Eindhoven University of Technology, The Netherlands: “Expanding thermal plasma CVD of ZnO:Al: plasma chemistry, growth modes and opto-electrical properties”
  • Alexandra Apostoluk, Lyon Institute of Nanotechnologies, France: “Solution-processed zinc oxide nanostructures for solar energy and sensing applications”
  • Martyn Pemble, University College Cork, United Kingdom: “A new look at an old material: doped ZnO for solar water splitting and for perovskite-based solar cells”
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On Ga2O3 : Wong Man Hoi
Authors : Man Hoi Wong 1, Kohei Sasaki 2,1, Yoji Morikawa 3, Akito Kuramata 2, Shigenobu Yamakoshi 2, Masataka Higashiwaki 1
Affiliations : 1 National Institute of Information and Communications Technology, Koganei, Tokyo 184-8795, Japan; 2 Tamura Corporation, Sayama, Saitama 350-1328, Japan; 3 Silvaco Japan Co., Ltd., Yokohama, Kanagawa 220-8136, Japan

Resume : Ga2O3 is an emerging wide-bandgap semiconductor for high power and high voltage electronics with potential applications in harsh environments. State-of-the-art Ga2O3 metal-oxide-semiconductor field effect transistors (MOSFETs) grown by molecular beam epitaxy were realized on unintentionally-doped (UID) beta-Ga2O3 (010) epilayers by Si-ion-implantation doping [1]. The high resistivity of UID Ga2O3 was harnessed for planar device isolation without mesa etching. Room temperature electron channel mobilities of 90-100 cm2/Vs with small in-plane anisotropy were extracted from large-gate MOSFET structures. Dielectric-passivated depletion-mode devices with a gate-connected field plate demonstrated a high off-state breakdown voltage of 755 V, a large drain current on/off ratio of over nine orders of magnitude at room temperature, dispersion-free output characteristics, and stable high temperature operation against thermal stress at 300 degrees Celsius [2]. The channel temperature and thermal resistance of these devices were systematically determined through temperature-dependent electrical measurements complemented by device simulations incorporating experimental Ga2O3 thermal parameters [3]. Such knowledge will be pertinent to the understanding of degradation mechanisms and improvement in reliability for Ga2O3 devices. [1] M. Higashiwaki et al., Semicond. Sci. Technol. 31, 034001 (2016). [2] M. H. Wong et al., IEEE Electron Device Lett. 37, 212 (2016). [3] M. H. Wong et al., ISCS 2016.

Authors : A. Fiedler, R. Schewski, M. Albrecht, M. Baldini, Z. Galazka, G. Wagner, K. Irmscher
Affiliations : Leibniz-Institute for Crystal Growth, Max-Born-Str. 2, 12489 Berlin, Germany

Resume : Doped beta-Ga2O3 layers have been grown homoepitaxially on (100) orientated substrates by metal organic vapor phase epitaxy (MOVPE) using either the shallow donor impurity Sn or Si. Conductivity and Hall effect measurements at room temperature show n-type conductivity. However, the measured electron concentrations between 5 x 10^17 1/cm³ and 2 x 10^19 1/cm³ indicate a strong electrical compensation and the electron mobilities of up to 40 cm²/(Vs) unexpectedly decline for low carrier densities. A possible explanation for this behavior comes from a structural analysis by transmission electron microscopy (TEM). It reveals that the layers contain a high density of planar defects consisting of twin lamellas and stacking faults. The lateral twin boundaries are incoherent and contain dangling bonds that trap charge carriers. This leads to charge accumulation and hinders lateral charge carrier transport. This behavior is in analogy to that of dislocation walls treated in [1]. Based on this model, we explain the observed steep decline in electron mobility at low carrier concentrations. Furthermore, the strong compensation of the donor dopants can, at least partly, be ascribed to the acceptor effect of the incoherent twin boundaries. [1] Krasavin, S. E.; Semiconductors 46, 598 (2012).

Authors : M. Feneberg, A. Janotti, M.D. Neumann, N. Esser, L. Artus, R. Cuscó, T. Yamaguchi, R. Goldhahn
Affiliations : Otto-von-Guericke Universität Magdeburg, Institut für Experimentelle Physik, Universitätsplatz 2, 39106 Magdeburg, Germany; University of Delaware, Department of Materials Science & Engineering, 212 DuPont Hall, Newark, DE, USA; Leibniz-Institut fur Analytische Wissenschaften?ISAS?e.V., Schwarzschildstr. 8, 12489 Berlin, Germany; Leibniz-Institut fur Analytische Wissenschaften?ISAS?e.V., Schwarzschildstr. 8, 12489 Berlin, Germany; Institut Jaume Almera (ICTJA-CSIC), Consejo Superior de Investigaciones Científicas, 08028 Barcelona, Spain; Institut Jaume Almera (ICTJA-CSIC), Consejo Superior de Investigaciones Científicas, 08028 Barcelona, Spain; Department of Electrical Engineering and Electronics, Graduate School of Engineering, Kogakuin University, 2665- 1 Nakano, Hachioji, Tokyo 192-0015, Japan; Otto-von-Guericke Universität Magdeburg, Institut für Experimentelle Physik, Universitätsplatz 2, 39106 Magdeburg, Germany

Resume : Polytypes of gallium oxide are a very promising class of materials for electronic device applications. For example, the high band gap of these oxides is related to high breakdown fields of the order of MV/cm. It is possible to stabilize ?-Ga2O3 by mist chemical vapor deposition on sapphire substrates. However, the optical properties of this metastable corundum-like phase have not yet been investigated thoroughly. Spectroscopic ellipsometry at room temperature has been applied to determine the ordinary (??) dielectric function of ?-Ga2O3. This corresponds to an electric field direction perpendicular to the optical axis (0001), which is the growth direction of the thin (about 400nm) ?-Ga2O3 films. The high energy spectral range up to 20eV has been investigated using synchrotron radiation. Several high-energy transitions have been resolved, which are consistent with comprehensive ab-initio calculations of the dielectric function that include the solution of the Bethe-Salpeter equation, i.e. Coulomb interaction between electrons and holes. The calculations suggest that ?-Ga2O3 is an indirect semiconductor with its valence band maximum between ? and K points of the Brillouin zone. Strong direct absorption onsets at around 5.3 and 6.2eV are found, only slightly higher in energy than the predicted band gap. Furthermore, the dispersion of the real part of the dielectric function is reported in the transparency region yielding a value for the dielectric limit ?? of around 3.95.

Authors : R. Schewski, M. Baldini, K. Irmscher, T. Markurt, B. Neuschulz, T. Remmele, T. Schulz, A. Fiedler, G. Wagner, M. Albrecht
Affiliations : Leibniz-Institut für Kristallzüchtung; Leibniz-Institut für Kristallzüchtung; Leibniz-Institut für Kristallzüchtung; Leibniz-Institut für Kristallzüchtung; Leibniz-Institut für Kristallzüchtung; Leibniz-Institut für Kristallzüchtung; Leibniz-Institut für Kristallzüchtung; Leibniz-Institut für Kristallzüchtung; Leibniz-Institut für Kristallzüchtung; Leibniz-Institut für Kristallzüchtung

Resume : Gallium oxide and its solid solutions with In2O3 and Al2O3 has been considered as a promising materials system for applications such as solar blind UV photo detectors and high power devices. Epitaxial growth of structurally perfect crystalline layers with defined doping is a prerequisite to fully use its potential for device applications. In contrast to III-Nitrides large diameter substrates grown from the melt by float zone edge defined film fed growth and Czochralski are available. Homoepitaxial growth therefore is a natural choice. Results from homoepitaxial growth have been achieved by methods like molecular beam epitaxy, halide vapor phase epitaxy, and metal organic vapour phase epitaxy. Though the (100) plane is an easy cleavage plane of the monoclinic lattice that can be easily prepared, growth rates seem to be negligible when using MBE. By MOCVD growth rates are an order of magnitude higher. However, the layers suffer from a high density of twins and stacking faults if growth conditions and miscut of the surface are not appropriate. These defects affect electrical properties active, i.e. they compensate doping and reduce the carrier mobility. In this contribution we present a detailed transmission electron microscopic and atomic force microscopy study on homoepitaxial growth of β-Ga2O3 by MOVPE on the (100) of β-Ga2O3 substrates with well-defined miscut. Our studies show that growth on vicinal surfaces with low miscuts proceeds through formation of two-dimensional islands. The aspect ratio of the width in b to width in c direction is b/c = 2, indicating an anisotropic diffusion of the ad atoms on the surface. TEM data reveal that the observed defects can be described as twins showing a c/2 glide reflection of the lattice as twin relation. With increasing off orientation regarding the a-plane surface normal of the substrate the twin density decreases. For layer grown with miscuts as high as 6° we found defect free layer showing perfect step flow growth. A quantitative evaluation of stacking fault densities from TEM data shows a dependency, typical for island nucleation processes on a vicinal surface. Assuming that stacking fault formation is based on the fact that islands nucleate either in the epitaxial relation or in the twinned orientation, a phenomenon well known as double positioning, we can apply nucleation theory in the mean field approximation [1,2] to fit our experimental results. We not only get excellent agreement to our experimental data on stacking fault densities as dependent on miscut but obtain a diffusion constant D of the ad-atoms on the (100) surface for the growth of β-G2O3. At our growth temperature of 850°C of D= 1.4*10-8 *cm2s-1 which is more than an order of magnitude lower than that of Ga on GaAs (D = 7 *10-7 cm2 s-1 estimated by Bietti et al. [3]). [1] J.A. Venables, Philos. Mag. 27, 697 (1973). [2] G.S. Bales, Surf. Sci. 356, L439 (1996). [3] S. Bietti, C. Somaschini, L. Esposito, A. Fedorov, and S. Sanguinetti, 114311, (2016).

Authors : A. Maertens ab, S. Margueron ab, F. Genty ab, A. Abrutis c, T. Belmonte d, P. Boulet d, J. Ghanbaja d, A. Talbi e, A. Bartasyte f
Affiliations : a Centrale Supélec, LMOPS EA 4423, 57070 Metz, France; b Université de Lorraine, LMOPS EA 4423, 57070 Metz, France; c University of Vilnius, Department of General and Inorganic Chemistry, 03225 Vilnius, Lithuania; d Université de Lorraine, Institut Jean Lamour, CNRS UMR 7198, Parc de Saurupt, F-54011 Nancy, France; e LIA LEMAC/LICS ? IEMN, EC Lille-CNRS UMR 8520, Cité Scientifique, 59652 Villeneuve d?Ascq, France; f FEMTO-ST Institute, CNRS UMR 6174, Université de Franche-Comté, 25030 Besançon, France;

Resume : Ga2O3 presents a gap of 4.9 eV [1]. Its conductivity can be modified by introduction of divalent/tetravalent ions [2]. Doped Ga2O3 presents widest band gap among oxide semiconductors and high breakdown voltage. Thus, it is studied for ultra-violet optoelectronics [3] and low-frequency transistors [4]. Nevertheless, undoped ?-Ga2O3 is a dielectric material and our films grown by chemical vapor deposition (CVD) did not present conductivity. In this work, SnO2 doping and alloying, as well as plasma treatment, supposed to modify the oxygen nonstoichiometry or the hydrogen doping, were investigated to clarify the conductivity mechanisms. Treatment by hydrogen plasma introducing protons is more effective way to ameliorate the conductivity than the creation of oxygen defects, which are too deep in the band gap to participate in conduction [5]. The films, with a thickness of about 150 nm, were grown by hot wire CVD under 10 Torr pressure on C-oriented sapphire substrates heated at 700°C. Ga2O3 films were epitaxial, as confirmed by pole figure, measured by X-ray diffraction. The effect of SnO2 alloying from 0 to 15 at.% on film texture and phase composition was investigated by recording ?/2? patterns by XRD. ?-Ga2O3 exhibited a preferential growth with (-201) family planes parallel to the surface plane, Moreover, the incorporation of SnO2 resulted in the extinction of (-201) and (-603) reflections, revealing the presence of a c-glide plane in doped Ga2O3. These results indicate that 15 at.% SnO2-Ga2O3, crystallizes with the space group C2/c whereas ??Ga2O3 adopts the C2/m space group. No impurity phases were observed. Study by transmission electron microscopy showed that ??Ga2O3 contained three growth variants of nanocrystals as already reported by Nakagomi [6]. Their presence can reduce the carrier mobility and partially explain the difference in conductivity between our films and layers grown differently. However, conductive films were obtained after treatments by argon and hydrogen plasma. The increase in conductivity was more significant after hydrogen treatment, which confirmed the calculations done by Varley et al. [5]. The modification of surface of SnO2-Ga2O3 films as well as the incorporation of hydrogen over the whole film thickness was confirmed by the secondary ion mass spectroscopy. In agreement with literature [3], we found that the conductivity was controlled by a hopping process at low temperature (10 K). Moreover, a strong absorption in the visible range was observed after the plasma treatment. An irreversible decrease in conductivity and an increase in transparency were induced by the temperature cycle from 300 to 500 K. The effects of Sn concentration, oxygen nonstoichiometry (deep level) and hydrogen doping are difficult to identify separately. However, the conductivity seems to be highly related to a polaron mechanism. [1] H. H. Tippins, ?Optical absorption and photoconductivity in the band edge of ?-Ga2O3?, Phys. Rev. 140, A316, 1965. [2] J. Franck, M. Fleischer, and H. Meixner, ?Electrical doping of gas-sensitive, semiconducting Ga2O3 thin films, Sensor Actuator B, 373-377, 1996. [3] M. Orita, H. Ohta, M. Hirano, and H. Hosono, ?Deep-ultraviolet transparent conductive- Ga2O3 thin films?, Appl. Phys. Lett. 77, 4166, 2000. [4] M. Higashiwaki, K. Sasaki, A. Kuramata, T. Masui, and S. Yamakoshi, ?Gallium oxide (Ga2O3) metal-semiconductor field-effect transistors on single-crystal-Ga2O3 (010) substrates?, Appl. Phys. Lett. 100, 013504, 2012. [5] J. B. Varley, J. R. Weber, A. Janotti, and C. G. Van de Walle, ?Oxygen vacancies and donor impurities in ?-Ga2O3?, Appl. Phys. Lett. 97, 142106, 2010. [6] S. Nakagomi and Y. Kokubun, ?Cross-sectional TEM imaging of ?-Ga2O3 thin films formed on c-plane and a-plane sapphire substrates?, Phys. Status Solidi A 210 (9), 1738, 2013.

Authors : E.Chikoidze [a], K. Akaiwa [b,c], K. Kaneko [b], S. Fujita [b], K. Ichino [c], H.J. von Bardeleben [d], Y. Dumont [a]
Affiliations : [a] GEMaC (Groupe d'Etudes de la Matière Condensée), Université de Versailles Saint-Quentin en Y. & CNRS, Université Paris-Saclay, Versailles, France ; [b] Department of Electronic Science and Engineering, Kyoto University, Kyoto, Japan ; [c] Department of Information and Electronics, Tottori University, Tottori, Japan [d] Institut des Nanosciences de Paris(INSP), Université Paris 6 & CNRS, Sorbonne Universités, Paris, France ;

Resume : Ga2O3 is a wide band gap semiconductor which occurs in different poly-types (alpha, beta, epsilon, delta, gamma). The polytype alpha-Ga2O3 , which is the stable form of Ga2O3 from room temperature up to its melting point, has already attracted attention more than half century ago due to its interesting optical and electrical properties: transparency in the deep UV and high n-type conductivity1 . Very recently alpha-Ga2O3 has become the object of intense research as it has been shown to be of high technological interest and has given rise to successful realization of microelectronic devices such as transparent field-effect transistor, high power devices, photodetectors and photodiodes [1-4]. Our work is dedicated to Ga2O3 , in the alpha- phase, one of the five phases known as thermally semi- stable. Highly crystalline Sn doped Ga2O3 thin films were synthesized by the mist CVD method [5]. We performed detailed studies of the influence of the Sn donor dopant on the optical and electrical properties of alpha-Ga2O3. Absorption coefficient and optical band gaps were estimated for the samples with different Sn concentrations, showing that doping does not deteriorate the UV-VIS-NIR transparency of the material. Resistivity and Hall effect measurements were done in 2K-400K temperature range and up to 9T magnetic field. The temperature dependence of the electrical conductivity shows that by varying the Sn donor concentration Ga2O3 can pass from insulator to a material with metallic conductivity. Photo-current has been measured as well. Different value and sign of magneto-resistance were shown for insulating, mixed and degenerated phases. By ESR spectroscopy we have determined the spin S=1/2 state and C3V point symmetry of the neutral Sn donor in a good agreement with the model of a simple SnGa center. [1] K.Matsuaki, H.Hiramatsu, K.Nomura, H.Yanagi, T.Kamiya, M.Hirano, H.Hosono, Thin films, 496,37, 2006 [2] M.Higashiwaki, K.sasaki, A.Kuramata, T.Masui, S.Yamakoshi, Appl.phys.lett.100, ,013504, 2012 [3] M.Zhong,Zh.Wei, X.Meng, F.Wu, J.Li, J.Alloys and compounds, 619, 572, 2015 [4] S.Nakagomi, T.Momo, S.Takahashio, Y.Kokubun, Appl.Phys.Lett, 103,072105, 2013 [5] K.Akaiwa and S.Fujita, Jpn.J appl.Phys. 51, 070203, 2012

On InGa2O3 : GALAZKA Zbigniew
Authors : Zbigniew Galazka
Affiliations : Leibniz Institute for Crystal Growth

Resume : Transparent semiconducting oxides (TSOs) constitute a class of materials with a unique combination of semiconducting behavior and full transparency in the visible and even down to ultraviolet spectrum as the result of wide energy gaps. Such properties make the TSOs suitable for emerging applications in electronics and optoelectronics. Bulk TSO single crystals cannot be readily obtained, because they suffer from a remarkable decomposition during preparation, what in combination with high melting points makes the crystal growth, especially from the melt, very challenging. This report will focus on bulk TSOs single crystals obtained by using new approaches and new methods that have been developed at the Leibniz Institute for Crystal Growth, as well as on structural quality and electrical / optical properties of the crystals. The bulk TSOs single crystals include β-Ga2O3, In2O3, MgGa2O4, BaSnO3 and InGaZnO4 grown from the melt, and SnO2 grown from the gas phase.

Authors : M. B. Maccioni(1), P. Alippi (2), V. Fiorentini (1)
Affiliations : 1) University of Cagliari, Italy 2) CNR-ISM

Resume : We report recent first-principles theoretical work on the In and Ga sesquioxides and their ternary alloy, a materials system for near to deep-UV large-breakdown and transparent- conducting materials. Firstly, a qualitative phase diagram is proposed over all the full composition range, where three structures –monoclinic 𝛽, layered-hexagonal, and cubic bixbyite– are competing for the ground state, and several regions of miscibility and phase separation interlace as function of composition, more or less independently of temperature. Electronic properties, including absorption anisotropy at low 𝑥, and a selection of interface band offsets are also obtained. Secondly, the metastable polar phase 𝜀-Ga2O3 is shown to be pyroelectric (i.e. locked in a non-switchable polarized structure) with a large ferroelectric-like polarization 0.23 C/m2 and a diagonal piezoelectric coefficient (0.77 C/m2) in line with those of III-V nitrides and II-VI oxides. The interface of 𝜀-Ga2O3 to GaN could, due to its large polarization difference have interesting potential for power applications.

Authors : Patrick Vogt, Oliver Bierwagen
Affiliations : Paul-Drude-Institut für Festkörperelektronik, Berlin, Germany.

Resume : In2O3 and Ga2O3 are n-type semiconducting oxides with wide band gaps of 2.7 and 4.5 eV, respectively. Recently, Ga2O3 has been recognized as a promising material for power electronics applications and UV detectors. These advanced applications typically require single crystalline films with well defined thickness and doping, which can be readily realized by molecular beam epitaxy (MBE). To largely extend their design space, the band-gap difference of In2O3 and Ga2O3 can be further exploited for band-gap engineering by alloying as well as formation of heterostructures by stacking layers with different composition. MBE growth conditions, such as growth rates and metal-to-oxygen flux ratio are important parameters to control crystal quality, composition, faceting, and point defects. Based on measured metal and oxygen fluxes, desorption and growth rate during growth as well as film composition after growth, our study provides a comprehensive picture on the kinetics and thermodynamics of the (InxGa1-x)2O3 growth by MBE for the entire range of compositions x. Formation and desorption of volatile suboxides, limiting the growth rate, is favored by high temperatures and metal-to-oxygen flux ratios. This incorporation-limiting kinetics is more severe for Ga2O3 than In2O3 due to the higher vapor pressure of Ga2O. Nevertheless, Ga is preferably incorporated during the alloy growth, which we attribute to a thermodynamic advantage due to stronger Ga-O bonds than In-O bonds.

Authors : V. Prozheeva 1, F. Tuomisto 1, H. von Wenckstern 2
Affiliations : 1 Department of Applied Physics, Aalto University, P.O. Box 11100, FI-00076 Aalto, Finland; 2 Universität Leipzig, Institut für Experimentelle Physik II, Halbleiterphysik, Linnéstraße 5, D-04103 Leipzig, Germany

Resume : An accurate knowledge of the compositional dependence on the properties of ternary alloy (InxGa1-x)2O3 is essential for mastering band-gap engineering and subsequent transfer to In-free TSOs. We present results obtained by positron annihilation spectroscopy in a sample with graded indium content grown by continuous composition spread (CCS) approach for pulsed-laser deposition (PLD) on c-plane sapphire [1]. Positron annihilation spectroscopy is a non-destructive method sensitive to neutral and negatively charged open volume defects [2]. The spatial distribution of indium was obtained by energy-selective X-ray spectroscopy. The positron data show decrease in vacancy-type defect concentration with lowering In content and indicate only one type of defects observed. The phase separation for x > 0.25 correlates with an extension of a defect site probably due to adding more oxygen vacancies next to the initial vacancies. Similar observations were made in case of InN [3] and in In2O3 and Ga2O3 separately [4, 5], where the cation-anion vacancy clusters have been found to be the main positron traps due to annihilations with the high-momenta electrons on the 2p shells of N or O. [1] H. von Wenckstern et al., Cryst. Eng. Comm. 15 (2013). [2] F. Tuomisto and I. Makkonen, Rev. Mod. Phys. 85 (2013). [3] C. Rauch et al., Phys. Rev. B 84 (2011). [4] E. Korhonen et al., Phys. Rev. B 90 (2014). [5] E. Korhonen et al., Appl. Phys. Lett. 106 (2015).

Authors : Theresa Berthold (1), Stefan Krischok (1), Marcel Himmerlich (1), Vladimir Polyakov (2), Volker Cimalla (2), Julius Rombach (3), Oliver Bierwagen (3)
Affiliations : (1) Institut für Physik and Institut für Mikro- und Nanotechnologien MacroNano, Technische Universität Ilmenau, PF 100565, 98684 Ilmenau, Germany; (2) Fraunhofer-Institut für Angewandte Festkörperphysik, Tullastraße 72, 79108 Freiburg, Germany; (3) Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany

Resume : In2O3 is a well-known material for conductometric gas sensors, where the electronic surface properties are of main interest. As grown In2O3 typically exhibits a high surface electron concentration, which is mainly influenced by gas adsorption [1]. The bulk electron concentration of In2O3 can be reduced by Mg-doping, and increased by vacuum annealing [2]. We characterize the surface composition and electronic properties of undoped and Mg-doped In2O3 films grown by PAMBE or MOCVD using photoelectron spectroscopy. We analyze the influence of surface reduction (vacuum annealing, UV illumination) and surface oxidation (oxygen plasma or ozone interaction) on formation/desorption of adsorbates or generation of defects as well as on variation in surface band bending, electron concentration and electric dipoles at the In2O3 surface. To clarify the effect of air humidity on the senor properties of In2O3, additional experiments focusing on water interaction combined with ozone oxidation were performed. Surface oxidation results in depletion/reduction of the surface electron density, which is partly reversed upon H2O adsorption and fully reversed after vacuum annealing. The experimental results are combined with Schrödinger-Poisson calculations to establish a quantitative analysis of the electron accumulation/depletion layer profile. [1] J. Rombach et al., Sens. Actuators B: Chem. (2016), doi:10.1016/j.snb.2016.03.079 [2] O. Bierwagen, et al., Appl. Phys. Lett. 101, 102107 (2012).

Authors : Julius Rombach (1), Alexandra Papadogianni (1), Theresa Berthold (2), Stefan Krischok (2), Marcel Himmerlich (2), Lutz Kirste (3), Oliver Bierwagen (1)
Affiliations : (1) Paul-Drude-Institut für Festkörperelektronik, Berlin, Germany; (2) Institut für Mikro- und Nanotechnologien Macro Nano®, Technische Universität Ilmenau, Germany; (3) Fraunhofer Institut für Angewandte Festkörperphysik, Freiburg, Germany

Resume : In2O3, traditionally used as transparent conductor and material for gas sensing, recently attracted attention as a semiconductor. It exhibits a surface electron accumulation layer (SEAL) which can dominate the transport properties of thin films. The SEAL is beneficial for gas sensing due to its concentration dependence on the surface adsorbate coverage [1]. In contrast, a SEAL can be detrimental for applications such as Schottky contacts were a depletion region is needed. Hence in order to improve existing and open up advanced applications, it is crucial to develop a deeper understanding and a precise control of the surface electronic properties of In2O3. To this end we employ Seebeck and Hall measurements [2] to disentangle the contributions of bulk & SEAL to the overall electrical transport properties of MBE-grown single-crystalline In2O3 films. Our results confirm that acceptor doping in high concentrations depletes the SEAL. We also demonstrate the influence of bulk & surface doping to establish control of the electron concentrations in the bulk and in the SEAL, respectively, taking into account the influence of the adsorbate coverage. XPS is used to directly probe the SEAL as well as to evaluate the relative position of the valence band with respect to the Fermi level on the surface in order to calculate the band bending. [1] J. Rombach et al, Sens. Actuators B: Chem. (2016), DOI: 10.1016/j.snb.2016.03.079 [2] A. Papadogianni et al, Appl. Phys. Lett. 107, 252105 (2015)

On Transparent Semiconductor Oxides: Materials Innovation : HAUTIER Geoffroy
Authors : Geoffroy Hautier
Affiliations : Université catholique de Louvain

Resume : Transparent conducting oxides (TCOs) are large band gap materials (to favor transparency) doped with electrons (n-type) or holes (p-type). TCOs are essential to many technologies from solar cell to transparent electronics and there is currently a large effort towards the discovery of new TCOs. I will present the results of a high-throughput computational search for new TCOs especially directed at p-type oxides. Focusing on low effective masses (leading to high mobility), large band gaps and dopability, I will show how thousands of oxides can be screened using various ab initio techniques (from density functional theory to GW) to find new potential high performance TCOs. I will discuss several unsuspected compounds with promising electronic structures and present preliminary experimental results. Beyond the description of those novel TCO candidates, I will chemically rationalize our findings, highlighting several design strategies towards the development of future high mobility TCOs.

Authors : David Caffrey, Emma Norton, Cormac O'Coileain, Leo Farrell, Brendan Bulfin, Christopher M. Smith, Igor V. Shvets and Karsten Fleischer
Affiliations : School of Physics and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College, The University of Dublin, Dublin 2, Ireland

Resume : Superlattice structures are a novel method of improving upon the optoelectronic properties of Transparent Conducting Oxide (TCO) structures. The invariability of the refractive index of TCO materials leads to reflection losses at the interfaces of transparent devices such as solar cells. The development of a transparent material or structure of tuneable refractive index would allow for the integration of anti-reflective coatings which would reduce such losses significantly, thus improving device efficiency. Previous attempts to modify the refractive index have been marred by the degradation of the electrical or optical properties of the tuned material. We demonstrate the novel use of a TCO/dielectric superlattice structure to achieve an effective medium of altered refractive index, while maintaining high values of transparency, conductivity and mobility. We demonstrate the efficacy of these superlattice structures on both amorphous InGaZnO4 and indium free ZnO:Al via TCO/SiO2 superlattices grown by magnetron sputtering. The effective refractive indices of the films were successfully tuned over a range of Δn≈0.2 with a decrease in conductivity of less than an order of magnitude. Mobility of the films was also well conserved a change of n≈0.2 resulting in a variation from 16.5cm2/Vs to 6cm2/Vs for the amorphous InGaZnO4/SiO2 superlattices, while the ZnO:Al/SiO2 superlattices varied from 7.3cm2/Vs to 1cm2/Vs. We will discuss the flexibility of our approach, allowing not only for a reduction of refractive index by using low refractive index interlayers (SiO2, MgO) but also an increase in n by using high refractive index e.g. TiO2 interlayers.

Authors : Christopher Sutton, Luca M. Ghiringhelli, Matthias Scheffler
Affiliations : Fritz-Haber-Institut der Max-Planck-Gesellschaft

Resume : Transparent conducting oxides (TCOs) are well-developed and commercialized class of wide-bandgap semiconductors that are crucial for the function of many electronic devices. Recent experimental work has demonstrated bandgap engineering in ternary (AlxGayIn1-x-y)2O3 over several ~ 3 eV by adjusting the ratio of In/Ga[1] and Ga/Al.[2] The focus of this work is an examination of the phase diagram for ternary (AlxGayIn1-x-y)2O3 materials using DFT-based cluster expansion (CE) models combined with fast stochastic optimization techniques (e.g., nested sampling). This combined computational approach allows for both an efficient search of the stable and metastable configurations for (AlxGayIn1-x-y)2O3 at various lattice types and the consideration of entropy on the relative stability of ternary TCOs. Statistical learning, in particular compressed sensing, is used to efficiently identify a structure-property relationship between the targeted properties (e.g., mobilities and optical transparency) and the fundamental chemical and physical parameters that control these properties. [1] Zhang et al., Solid State Commun, 186, 28 (2014). [2] Ito et al., Jpn. J. Appl. Phys., 51, 100207 (2012); Zhang et al., Appl. Phys. Lett., 105, 162107 (2014).

Authors : Aurélie Rexach, Dr Alec Gunner
Affiliations : TWI Ltd, Granta Park, Great Abington, CB21 6AL, Cambridge (UK)

Resume : Thin films made from transparent conducting oxides (TCO) are used in a variety of optoelectronic devices such as flat panel displays (e.g. LCD), photovoltaic cells and light-emitting diodes (LEDs). In 2012, 93% of the transparent conductive coatings market used indium tin oxide (ITO) due to its high electrical conductivity and high light transmission. However, indium is a scarce metal and hence presents two main drawbacks: high price due the ever-growing demand and limited availability. Thus, the INFINITY project aims to develop an innovative way to produce an indium-free TCO layer applicable to plastic substrates. This raises significant challenges: the design of a highly conductive TCO layer that could compare to ITO with low temperature curing. There is therefore a need for tailored, high-purity oxide metal precursors to be processed using a sol-gel approach to form an oxide-precursor ink suitable for deposition and laser curing and heat treatment. We will present the process, the challenges it addresses and raises and some preliminary public results of the INFINITY project. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 641927.

Authors : Jonathan Crêpellière, Petru Lunca Popa, Naoufal Bahlawane, Renaud Leturcq, Damien Lenoble
Affiliations : Material Research and Technology (MRT) Department, Luxembourg Institute of Science and Technology (LIST), 5 Avenue des Hauts-Fourneaux, L-4362 Esch-sur-Alzette, Luxembourg

Resume : Recently, low-temperature synthesis of highly conductive and transparent CuCrO2 with the delafossite crystal structure has been demonstrated using metal-organic chemical vapour deposition (MOCVD) [1] and spray pyrolysis [2], with figure of merits among the highest for p-type transparent oxide semiconductors. Although the material is grown without intentional doping, the electrical properties are comparable to Mg-doped CuCrO2 [1-4]. Moreover they show a strong Cu/Cr non-stoichiometry, obtained in a wide range of growth parameters [1,4]. In order to investigate the origin of the high doping in MOCVD-grown CuCrO2, here we investigate thermoelectric properties of thin films obtained with a large range of synthesis conditions (temperature, oxygen partial pressure, precursor concentration and fraction, post-growth annealing). Seebeck coefficient and electrical conductivity have been measured simultaneously in a temperature range of 140-400 K. The data are directly compared to the mostly used carrier transport models, mainly comparing band conduction and small polaron hopping. This analysis may favour the band conduction in our system, with a strongly localized band edge explaining the low observed carrier mobility. [1] J. Crêpellière et al., J. Mater. Chem. C, 2016, 4, 4278. [2] L. Farrell et al., J. Mater. Chem. C, 2015, 4, 126. [3] L. Farrell et al., Phys. Rev. B, 2015, 91, 125202. [4] P. Lunca Popa et al. (submitted).

Authors : Blomberg T., Huotari H., Tuominen M., Lindroos L.
Affiliations : ASM Microchemistry Ltd.

Resume : Nanocomposites are composite materials with a characteristic size of one or more phases less than 100 nm. Nanocomposites may have electrical, optical and mechanical properties that differ substantially from their bulk counterparts due to their very large surface to volume ratios. We report the synthesis of metal matrix nanocomposite thin films consisting of TiF3 nanoparticles embedded in TiN matrix with the atomic layer deposition (ALD) method. TiF4+Si2H6/Si3H8+NH3 process at 350-370 °C led to nanocomposite TiF3:TiN thin films with the embedded TiF3 nanoparticles in the size range of 2-50 nm. The films grown on quartz wafers were conductive and transparent in the visible spectral range. The resistivities of the films could be controlled by the (TiF4+Si2H6)/NH3 pulsing ratio. Transparency of the films correlated with the resistivity of the films, namely the more transparent the films were, the higher the resistivities. About 4 cm2 area photovoltaic cells with TiF3:TiN/SiO2(1.5-20nm)/p-type Si(1-85 Ωcm)/SiO2(1.5-20nm)/TiN structures resulted in 0.10-0.45 V open circuit voltage and 1-2.5 µA current flow into a 120 Ω load resistor under halogen lamp (Osram 50 W, 240 V bulb, 2800K) illumination, measured with Fluke 189 voltmeter. The mechanism of the photovoltaic effect in these structures is not known in detail, but it is suggested that the TiF3:TiN nanocomposite functions as a partly transparent conducting electrode on the silicon wafer forming a MIS type silicon photovoltaic cell. This new material and its derivatives may have multiple applications in current and future photonic devices.

On Deposition : DUTSON James
Authors : J.D. Dutson, S.A. Thornley, P.J. Hockley, S.G. Rand, M.J. Thwaites
Affiliations : Plasma Quest Ltd, Unit 1B Rose Estate, Osborn Way, Hook, Hants, UK. RG27 9UT

Resume : This work describes the development of a large area coating deposition tool using a remotely generated plasma for the deposition of transparent conducting oxides (TCOs). Previous work [1] has demonstrated that enhanced TCO properties for an ambient temperature process can be achieved by using a deposition technology that utilises a remotely generated plasma for sputter deposition (HiTUS). However, HiTUS is limited in scale with typical disc target areas 100mm in diameter. Using the same paradigm of remote generation but a novel geometry of the plasma to form a large-area plasma in close proximity to a planar target, it is possible to sputter targets with area of 400x120mm. Using an inline translation process, substrates with areas of 300x300mm have been coated. This technology, known as the extended planar plasma system (EPPS) is capable of static deposition rates in excess of 400nm/min for metals. Using a reactive deposition process, it is possible to deposit aluminium-doped zinc oxide with similar properties to those achieved with the HiTUS technology, with resistivity of <2x10-3 and peak optical transparency of the film >98% when measured relative to the substrate. Furthermore, the fundamentals of the plasma generation can enable targets of greater length to be used, further enhancing its potential capability. The work will outline the EPPS technology and compare the geometry and plasma generation with that of the HiTUS technology. Material properties of the TCO materials will be compared between the two systems. Finally, these coatings will be evaluated for use in a variety of applications including photovoltaic systems and light emitting diodes. This research has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 641864 (INREP). [1] Wakeham et al., Thin Solid Films 518 (2009) pp1355-1358.

Authors : Thiago Martins Amaral, Sabine Heusing, Peter König, Peter William de Oliveira
Affiliations : INM- Leibniz Institut für Neue Materialien gGmbH Saarbrücken, Germany

Resume : ITO (In2O3:Sn) is a transparent conducting oxide (TCO) often employed as electrode in displays and many other optoelectronic devices.Its limited availability fomented research and led to the discovery of other TCOs such as TiO2:Nb, ZnO:Si (SZO) and ZnO:Al (AZO), nowadays also applied in various devices. Nevertheless, although the price of these In-free TCOs are lower than for ITO, the processes involved in coating substrates are still slow and expensive due to the necessity for vacuum. By contrast, the possibility of directly printing TCOs would allow faster and cheaper roll-to-roll fabrication. The development of suitable TCO inks addresses many challenges regarding interactions between the ink components,between the ink and the printing system and between the ink and the substrate. Moreover, solvent evaporation and curing conditions play an important role in the deposition of In-free TCO layers on plastic substrates. SZO and AZO inks that meet the requirements of inkjet printing were developed. Their viscosity, density and surface tension were adjusted by proper mixture of solvents to allow printing in nozzles with less than 70 μm diameter. Moreover, the solvents were also selected to suppress the coffee ring effect by inducing Marangoni flow that affects the particle spatial distribution during evaporation. In-free TCO lines with improved optical properties and room temperature processing were printed on flexible substrate without necessity of vacuum, which is a promising perspective for printed electronics. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 641927.

Authors : Nicholas Cavallari, Greta Rosa, Alessio Bosio, Roberto Fornari, Edmondo Gilioli and Francesco Pattini
Affiliations : N. Cavallari1, 2, G. Rosa1, A. Bosio1, R. Fornari1, 2, E. Gilioli2 and F. Pattini2 1 Department of Physics and Earth Sciences, University of Parma, Parco Area delle Scienze 7/A, 43124 - Parma, Italy, Phone: +39-0521-905222; 2 IMEM, Parco Area delle Scienze 37/A, 43124 - Parma, Italy - Phone: +39-0521-26911;

Resume : CuGaO2 belongs to the delafossite family and recently received consideration as transparent conducting oxide (TCO) for photovoltaic (PV) and electronic applications. One attractive feature of this oxide is given by the possible p-type conductivity, which is very unusual by other types of oxides. In this work we report on the deposition of transparent CuGaO2 thin films, by RF reactive sputtering in (Ar + O2) ambient, on soda lime glass (SLG) and c-oriented sapphire substrates. We tested different home-made targets with variable Cu/Ga ratios and found that the correct Cu/Ga composition in the layer was routinely achieved by using a CuGa2 target based on the epsilon-phase of the Cu-Ga binary system. The X-ray analysis of as-deposited films on SLG showed that the CuGaO2 delafossite phase is made of nano-grains (28-35 nm), preferentially oriented along the (101) direction of the rhombohedral phase (R-3m space group). This result is obtained by deposition at 500 °C, directly on SLG or on a template formed by a thin layer of pre-deposited B2O3. At this temperature, both these substrates exhibit a quasi-rheotaxial behavior so that CuGaO2 resulted deposited on a quasi-liquid surface which promotes a higher surface diffusion of the deposited species. This enhanced diffusion helps the formation of the delafossite phase at this relatively low substrate temperature. On the other hand, films directly deposited at 500 °C on solid sapphire or silica, converted to delafossite phase only after an annealing at 750 °C. In this case, however, in addition to the rhombohedral (101) direction, also the (102) and the (202) orientations of the hexagonal phase are present.

Authors : Sabine Heusing, Thiago Martins Amaral, Peter König, Peter William de Oliveira
Affiliations : INM - Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbruecken, Germany

Resume : Transparent conductive oxides (TCO) are widely used as transparent electrodes and are usually fabricated by vacuum processes. Direct printing of TCO patterns could offer an enormous advantage since the multi-step process for patterning and etching would be avoided. In this work TCO inks which can be printed by gravure and ink-jet printing process were developed and TCO coatings and patterns were printed. The inks were fabricated by dispersion of TCO nanoparticles in a solvent with addition of a binder and further additives (e.g. photo-initiator). In order to obtain TCO coatings with low resistivity and high transmission, the composition of the TCO ink was varied by changing the binder, the solvents and the additives. The resistance was studied after UV curing and after various thermal post-treatments. In addition the behaviour of the resistance was studied during the UV curing process. Furthermore the untreated deposited coating and the UV cured coatings were studied after certain UV doses by FTIR spectroscopy, in order to track the involved chemical reactions. The optical properties of the coatings were studied by UV-VIS-NIR spectroscopy and the morphology was studied by SEM. As TCO material, ITO nanoparticles were employed. It is expected that the results can be transferred to other TCO similar inks. This is the aim of further investigations, which is to develop an innovative way to produce indium-free TCO layers and patterns by direct printing process. This work was conducted as part of the INFINITY project which has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 641927.

Authors : Rita Branquinho, Emanuel Carlos, Ana Santa, Daniela Salgueiro, Asal Kiazadeh, Pedro Barquinha, Rodrigo Martins, Elvira Fortunato
Affiliations : i3N/CENIMAT, Department of Materials Science, Faculty of Science and Technology, Universidade NOVA de Lisboa and CEMOP/UNINOVA, Campus de Caparica, 2829-516 Caparica, Portugal

Resume : Oxide based electronics have been well established as an alternative to silicon technology, however typical processing requires complex high vacuum equipment which is a major drawback, especially when targeting low cost applications. Recently, there has been remarkable development in solution processed inorganic metal oxide materials for high-performance thin-film-transistors (TFTs) with impressive results.[1] The possibility to deposit the materials by low cost techniques such as inkjet printing has drawn tremendous interest in solution processible materials for electronic applications. However, high processing temperatures incompatible with flexible substrates are still required. To overcome this issue solution combustion synthesis has been recently pursued. Taking advantage of the exothermic nature of the reaction as a source of energy for localized heating, the precursor solutions can be converted into oxides at lower process temperatures (Figure 1). Theoretically this can be applied to any metal ions to produce the desired oxide, opening unlimited possibilities to materials’ composition and combinations.[2] The chemistry of the redox reaction is determinant for the thermodynamics of the oxide formation; namely the nature of the reagents and the fuel/oxidizer ratio, which is based on propellant chemistry. Other variables, like reagents concentration, solvent and pH, must also be considered.[3,4] Solution combustion synthesis has been applied for the production of high κ dielectrics; Al2O3 and HfO2, for electronic devices and applications in oxide based TFTs. The properties and quality of produced thin films are highly dependent on the precursor solution characteristics; hence the influence of several processing parameters such as the nature of metal salt precursor, organic fuel and solvent were studied for different solutions concentration and annealing processes. Although the precursor solution degradation/oxide formation mechanism is not yet fully understood, we demonstrate that high performance devices can be obtained with solution processed metal oxide thin films annealed at low temperatures compatible with flexible electronics. 1. B. Du Ahn, H.-J. Jeon, J. Sheng, J. Park, and J.-S. Park, Semicond. Sci. Technol., 6, 064001 (2015). 2. M.-G. Kim, M. G. Kanatzidis, A. Facchetti, and T. J. Marks, Nat Mater, 5, pp. 382–388 (2011). 3. R. Branquinho, D. Salgueiro, L. Santos, P. Barquinha, L. Pereira, R. Martins, and E. Fortunato, ACS Appl. Mater. Interfaces, 6, 195592–9 (2014). 4. R. Branquinho, D. Salgueiro, A. Santa, A. Kiazadeh, P. Barquinha, L. Pereira, R. Martins, and E. Fortunato, Semicond. Sci. Technol., 30, 024007 (2015).

Authors : M. Chaves, R. Ramos, S. F. Durrant, J. H. D. da Silva, T. F. da Silva, and J. R. R. Bortoleto
Affiliations : São Paulo State University (UNESP), Av.3 Março 511 Sorocaba SP, Brazil; São Paulo State University (UNESP), Av. Eng. Luiz Edmundo C. Coube Bauru SP, Brazil; São Paulo University (USP), Rua do Matão Trav. R187 SP, Brazil

Resume : Aluminum zinc oxide (AZO) has been used as transparent and conducting oxide film in solar cells and electrochromic devices. Also, AZO thin films have great potential for applications in flexible display technology. In this work, structural properties and aluminum doping efficiency of AZO thin films grown by rf magnetron sputtering at temperatures lower than 150ºC have been investigated. AZO thin films were deposited using both ceramic and metallic targets at different oxygen-metal ratios. Surface morphology was measured with atomic force microscopy (XE-100, Park Systems) operating in air. All AFM images of the films were analyzed using fractal and scaling concepts. The orientation and size of crystallites were estimated using X-ray diffraction (D/MAX-2100/PC, Rigaku). Optical gap was deduced from the Uv-Vis-NIR spectra (Lambda 750, Perkin Elmer). The chemical composition and density of films were obtained by Rutherford backscattering spectroscopy (RBS) with 2.2 MeV He ions. Electrical properties were characterized by the four-point probe method and Hall measurements (HMS 3000, Ecopia). Our results suggest that the scattering due to deactivate Al atoms and grain boundaries are of the same order, constraining the electrical mobility lower than 30 cm2/Vs.

Authors : Jung-Dae Kwon, Jong-Joo Rha, Kee-Seok Nam
Affiliations : Korea Institute of Materials Science

Resume : Copper oxide (CuOx) films were grown at a relatively low temperature (100 °C) by atomic layer deposition (ALD). Hexafluoroacetyl-acetonateCu(I)(3,3-Dimethyl-1-butene) ((hfac)Cu-(I)(DMB)) and ozone (O3) were used as the copper precursor and oxidant, respectively. It is shown that stable phases of CuOx are obtained through rapid thermal annealing (RTA) in air. After annealing at various temperatures (200–500 °C), different p-type band structures and electron binding information are obtained. X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE) studies indicate that the major copper oxidation state changes from 1+ to 2+ during thermal treatment. Thin film transistors (TFTs) incorporating the ALD-grown CuOx semiconductors are evaluated, and an unusually high p-type device performance is observed, with a field effect mobility of 5.6 cm2/V s after annealing at 300 °C.

Authors : J. Priesol (1), A. ?atka (1), I. Girgel (2), D. W. E. Allsopp (2), P. A. Shields (2)
Affiliations : 1. Institute of Electronics and Photonics, Slovak University of Technology in Bratislava, Ilkovi?ova 3, 812 19 Bratislava, Slovakia 2. Department of Electronic and Electrical Engineering, University of Bath, Claverton Down, BA2 7AY, Bath, UK

Resume : Core-shell (CS) nanorods (NR) are of focused interest for lighting applications allowing growth of active LED regions on nonpolar GaN planes. This way, LED structures with reduced defect density and increased external quantum efficiency can be produced. To ensure proper functionality of these devices, a good integrity of transparent conductive oxide (TCO) with the contact layer of the 3D structure has to be satisfied. In this contribution we report on the electrical and optical characterization of uncovered and TCO-covered GaN CS NRs by cathodoluminescence (CL) and electron beam induced current (EBIC). CL has been used to evaluate the Mg incorporation in the p-GaN shell forming the p-contact layer. Good homogeneity was observed at low and medium Mg doping, whilst a high dopant flow rate led to decrease of CL uniformity. The formation of a p-n junction and its shape have been examined by spectral CL mapping of cleaved CS-NRs. Additional experiments on TCO-free CS-NRs by EBIC showed current collection was localized very close to the metallic probe tip, the effect attributed to a relatively high resistivity parallel to the p-n junction due to the p-type outer shell being extremely thin and hence partially or wholly depleted of charge carriers. Deposition of the TCO contact layer resulted in dramatically improved carrier collection, evidencing formation of a low resistance ohmic contact. Comprehensive EBIC analysis revealed variations in the TCO properties depending on deposition conditions, as well as defects at the apex and m-plane edges of the GaN NRs. Finally, EBIC maps measured on a NR cross-section directly proved the formation of a p-n junction within the CS NRs. This research has received funding from the European Union?s Horizon 2020 research and innovation programme under the grant agreement No 641864 (INREP).

Authors : K. Elen (1,2), S. Nagels (3,4), H. Penxten (5), L. Lutsen (1), W. Deferme (3,4), A. Hardy (1,2), M. K. Van Bael (1,2)
Affiliations : (1) IMEC vzw, division IMOMEC, Wetenschapspark 1, B-3590 Diepenbeek, Belgium - (2) Hasselt University, Institute for Materials Research (IMO), Inorganic and Physical Chemistry, Agoralaan Building D, B-3590 Diepenbeek, Belgium - (3) Hasselt University, Institute for Materials Research (IMO), Functional Materials Engineering, Wetenschapspark 1, B-3590 Diepenbeek, Belgium - (4) Flanders Make vzw, Oude Diestersebaan 133, B-3920 Lommel, Belgium - (5) Hasselt University, Institute for Materials Research (IMO), Organic and Bio-Polymer Chemistry, Agoralaan Building D, B-3590 Diepenbeek, Belgium

Resume : Metal nanowire networks are a promising concept for replacing ITO in transparent electrodes for a range of optoelectronic devices. In these networks, the nanowires conduct charge carriers, while the open areas allow the transmission of light. Metal nanowires are both printable and achieve a performance equivalent to ITO upon thermal processing at temperatures below 150°C which make them ideal for depositing transparent electrodes on plastic substrates. For this contribution, silver nanowires (AgNWs) were synthesized using a polyol synthesis method. Various formulations containing AgNWs were prepared and their rheological behavior was assessed in view of screen printing. The most promising formulations were selected to print test features on PET substrates and the electrical and optical characteristics of these features were measured by a Van der Pauw method and UV-Vis spectroscopy respectively. By the addition of AgNWs to a PEDOT-based formulation, the sheet resistance of the printed features can be decreased from ca. 200 Ohm/sq to values below 40 Ohm/sq, indicating that a nanowire network improves the conductivity. However these features appear blue due to the absorption of (infra-)red light by PEDOT. The optical properties can be significantly enhanced by replacing the PEDOT-based formulation by a cellulose-based formulation. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 641864.

Authors : Do Hwi Park, Ho Young Jun, Si Ok Ryu*
Affiliations : Yeungnam University

Resume : In order to increase the environmental compatibility and commercial potential of thin film solar cells based on Cu(In,Ga)Se2 (CIGS), a device without hazardous Cd is desirable. In2S3, Zn(O,S), ZnMgO are alternative materials for currently being used CdS buffer layer. Zn(O,S) is considered as the most promising alternative substance among them because of its non-toxicity and its possible band gap engineering in the range of 3.0-3.7eV depending upon the ration of O/S. The aim of this study is to fabricate Cu(In,Ga)Se2 devices with Zn(O,S) buffer layers deposited by a modified CFR process with a controlled variation of annealing temperature. The modified CFR process is possible to control the particle size and thickness of the thin films through adjusting flow rate, precursor solution temperature, and deposition time. The films were characterized X-ray diffraction (XRD), Scanning electron microscopy (SEM) and UV-vis spectroscopy. XRD analysis was employed to identify the phase for obtain thin films. SEM was used to provide the detailed information for particle size and surface morphology. Energy band gap was estimated by UV-vis spectroscopy. The photovoltaic performance of the Cd-free structured B:ZnO/Zn(O,S)/CIGS/Mo thin film solar cells was carried out in this study. Current-voltage measurement for the device were carried out at 25℃ using a solar simulator (K3000, McScience) with an AM 1.5 under an irradiation intensity of at 100mW/cm2.

Authors : Yujin Kim, Geumbi Mun, Hyein Yeom, Prof. Sang-Hee Ko Park
Affiliations : Display R&D center, Samsung Display & Dept. of Materials Science and Engineering, KAIST; Dept. of Materials Science and Engineering, KAIST; Dept. of Materials Science and Engineering, KAIST; Dept. of Materials Science and Engineering, KAIST

Resume : As recent display market has rapidly evolved into ultra-high resolution, technology of minimizing RC delay and establishing high mobility, high integrated, and reliable TFT has become very important. Accordingly, self-aligned structured oxide TFT should be developed in order to minimize RC delay which impedes transmission of electrical signal. For that reason, applying dry etching process, which is known as a useful method to pattern even submicron structure, must be necessary. However, at least two times of dry etching processes on exposed oxide semiconductor are inevitable during fabrication process of self-aligned structured TFT. One is patterning gate insulator layer deposited directly on active layer, and the other is opening contact holes with dry etching inter-layer dielectric. For dry etching Al2O3, SiO2 or SiNx dielectric layers, Cl2, CF4 or Ar gases are mainly used which produce Cl ion, F ion or Ar ion respectively, and it was assumed that those ions may cause any kind of effects on exposed active layer. In this study, we fabricated top gate structured IGZO TFT mimicking self-aligned structure to examine generated ion or plasma effect on oxide semiconductor. We intentionally applied various plasma damages simulating dry etching gas on exposed channel area, and investigated the electrical characteristics of final transistors. Helicon plasma system which is high density plasma system was used for this study, and the tendency for changes of the TFT properties such as mobility, S.S and hysteresis depending on manipulation of exposure time of dry etching process or quantity of reaction gas.

Authors : SangTae Kim, KiJune Lee, YeonWoo Shin, TaeJung Gim and JaeKyeong Jeong
Affiliations : Dept. of electronics and Computer Engineering, Hanyang University, Seoul 133-791, Korea

Resume : Transition tantalum induced crystallization of amorphous zinc tin oxide (a-ZTO) was observed at low temperature annealing of 300°C. Thin-film transistors (TFTs) with an a-ZTO channel layer exhibited a reasonable field-effect mobility of 12.4cm2/Vs, subthreshold swing (SS) of 0.39 V/decade and Threshold voltage (VTH) of 1.5 V. A significant improvement in the field-effect mobility (up to ~33.5cm2/Vs) was achieved for crystallized ZTO TFTs. The degree of lattice ordering was enhanced along the depth direction from the TaOx/ZTO interface toward the front channel region. This may suggest that the nucleation and grain growth were initiated near the TaOx/ZTO interface. The plausible rationale in the case of the nickel (Ni)-induced crystallization of TiO2 was suggested based on the donation of valence electrons of Ni into Ti-O bond. An analogous mechanism would be envisaged for the Ta-induced crystallization of ZTO film. The electron transfer from the Ta with a low electronegativity to the anti-bonding orbital of M-O (M = Zn or Sn) bond can weaken the M-O bonds in amorphous ZTO. The rearrangement of M-O bonds will be facilitated by the thermally broken M-O bond where the thermodynamic driving force comes from the lower Gibbs free energy of the crystalline ZTO compared to that of the amorphous state. It is expected that the high degree of lattice ordering near the channel/gate dielectric interface contributes to the higher mobility of the resulting transistors.

Authors : Yun-Been Na, Jeong Jin Park, Chan-Hwa Hong, Chang-Ho Lee, Woo-Seok Cheong
Affiliations : Korea University of Science & Technology, Daejeon 34113 Korea; Electronics and Telecommunications Research Institute, Daejeon 34129, Korea

Resume : In recent year, amorphous oxide thin film transistors(TFTs) have attracted interest of applications for flexible organic light emitting diodes(OLEDs). For reasonable oxide TFTs, the requirements such as high mobility and good stability at low temperatures should be satisfied. In this study, we chose double channel layers to solve the issues of oxide TFTs at low temperature and we successfully fabricated top gate ZITO/ ZITO:AlZr TFTs. After low-temperature annealing process at 250℃, Vth of -0.75V, SS of 0.16V/decade and mobility(uFE) of 18.8 cm2/V s were achieved. At the PBTS(positive bias temperature stress) test, the oxide-TFT exhibited △Vth of 0.42V at 40℃ for 1hour.

Authors : Fahad Azad 1, 2, Shichen Su 1, Caiqin Luo 1, Kaimin Shih 3, Changzhong Liao 3, HangKong Li 3, Muhammad Younas 4, Francis C. C. Ling 1
Affiliations : 1 Department of Physics, The University of Hong Kong, Pokfulam, Hong Kong, P. R. China 2 School of Natural Sciences, National University of Sciences and Technology, H-12 Islamabad, Pakistan 3 Department of Civil Engineering, The University of Hong Kong, Pokfulam, Hong Kong, P. R. China 4 Electronic and Magnetic Materials Group (EMMG), PD, PINSTECH, PO Nilore, Islamabad, Pakistan

Resume : Transparent conducting ZnO:Er films (150-200 nm thick) were grown on (001) sapphire substrate using pulsed laser deposition (PLD) technique. The effect of Er doping concentration, substrate temperature, oxygen partial pressure during growth and post growth annealing temperatures on the structural, electrical, morphological, and optical properties of ZnO:Er films were systemically investigated. The XRD spectra grown at all the substrate temperatures (namely 300, 450 and 600˚C) and different oxygen partial pressures revealed the single-phase material with (002) orientation. An optical transmittance of ~97% in the wavelength range 400-800 nm and a low resistivity of 5×10-4 Ω cm were achieved for the Er0.01Zn0.99O sample grown without oxygen and at the substrate temperature of 600˚C. Post growth annealing of the samples in the temperature range of 650-900 oC turned the film to highly resistive, and thermally activated the 4f intra-shell transitions of Er thus revealing the emissions at the wavelengths of ~560 nm and 650-700 nm in the low temperature (10 K) PL spectra.

Authors : Peter Fischer [1], Edda Rädlein [1], Harald Hoppe [2], Roland Rösch [2]
Affiliations : [1] TU Ilmenau, Institut für Werkstofftechnik, Gustav-Kirchhoff-Str. 6, 98693 Ilmenau, Germany; [2] Uni Jena, Center for Energy and Environmental Chemistry Jena, Philosophenweg 7a, 07743 Jena, Germany

Resume : The present work deals with the solution of the problem to produce conductive, semitransparent and liquid processable metal oxide layers. The standard used electrode at the moment is Indium Tin Oxide (ITO). ITO has a high transmittance [88%] and conductivity (11 Ω/□), but because of the high cost of indium an alternative has to be found. Niobium-Doped Titanium Oxide (TNO) showed very good transparency (75%) and conductivity (79 Ω/□) sputtered on a glass. However, sputtering causes high production costs. In contrast, sol-gel process provides simplicity, low cost, and feasibility, also proving as a precise approach to control doping concentrations The lowest reported resistivity with sol-gel is 40.000 Ω/□ with a transparency of 80% by Elen et al. In this work the conductivity and transparency of TNO layers produced by sol-gel technique are investigated. The samples were coated by spin-coating. The thickness of the samples was adjusted with different spin speeds. The conductivity of the samples was measured using a four-point set-up. Transmittance spectra were recorded in the wavelength from 190 to 800 nm. The samples were heated in a rapid thermal processing furnace (RTP) under different atmospheres, temperatures and time. A pre-heating of the films on a hot plate at 80°C was necessary for all the substrates. The best heating procedure was when the sample is first pre-heated and with a further step in a N2/H2 atmosphere with 1000°C for 10 minutes annealed in the RTP. In this case a good sheet resistance of 175 Ω/□ was reached, which enables the use of the TNO processed with sol-gel as electrode in optical devices. The transparency of 35% in the visible range is still to be improved.

Authors : Nuri On*, Sangtae Kim*, Kijun Lee*, Hyeonju Soel* and Jae Kyeong Jeong*
Affiliations : Department of electronics and computer Engineering, Hanyang University, Seoul

Resume : The ZnO-based oxide semiconductor thin film transistors (TFTs) have a strong properties such as low temperature processing, high mobility, excellent uniformity, and good transparency to visible light to be used in electronic devieces including the thin film transistor back planes for flexible display or active matrix organic light emitting diodes (AMOLEDs). However, the device stability is one of major issue of metal oxide TFTs. The mecahism of the device instability is chrge trapping in the gate didelectric, ambient interaction and oxygen vacancy model [1]. This study examuned effect of positive gate stress and negative bias illumination stability in indium gallium zinc oxide (IGZO) TFTs, fabricated various oxygen ratio(63%,75% and 80%). The IGZO TFTs appear the change of threshold voltage in the transistor channel layer and electrical properties with different O2 ratios [2,3]. In this study, the threshold voltage shift (ΔVth) under positive bias stability was increased relying on increasing oxygen ratio. Also, The threshold voltage shift (ΔVth) under Negative bias illumination stability, 63% and 75% oxygen ration was higer than 80% under 80°C. However, 75% oxygen ratio was lower than 63% and 80% over 100°C.

Authors : Hyoeun Kim, Vasudeva Reddy Minnam Reddy, Haeyun Cho, Myeongho Kim, Dong-seob Jeong, Babu Pejjai and Chinho Park*
Affiliations : School of Chemical Engineering, Yeungnam University, 280, Daehak-ro, Gyeongsan 38541, Republic of Korea

Resume : Low-cost and earth-abundant tin sulphide films have been grown by effusion sulphurization process using sputtered tin precursor layers. The effect of sulphurization temperature (Ts) that varied in the range of 250–550 °C for a fixed sulphurization time of 30 min on SnS film was studied through various characterization techniques. The X-ray diffraction measurements indicated that all the grown films had the (111) crystal plane as the preferred orientation and exhibited orthorhombic crystal structure. The optical energy band gap values were estimated using the transmittance spectra and found to be varied from 1.1 eV to 1.5 eV with Ts. SnS based solar cells were fabricated with the structure of Glass/Mo/SnS/CdS/i-ZnO/Al:ZnO:Al/Ni-Ag. The fabricated solar cells showed conversion efficiency > 2.6%. The details are discussed with growth sulfurization temperature on earth-abundant solar cells.

Authors : K. Cavanagh [1], S. Thornley [2], J. Dutson [2], M.A. Hopkins [1], M. Thwaites [2], D. W. E. Allsopp [1]
Affiliations : [1] Department of Electronic and Electrical Engineering, University of Bath, Claverton Road, BA2 7AY, Bath, UK [2] Plasma Quest Ltd, Unit 1B Rose Estate, Osborn Way, Hook, Hampshire, RG27 9UT

Resume : GaN-based LEDs often employ a thin annealed Ni/Au layer as a transparent p-contact as a good ohmic contact is formed, however this suffers from low transmittance (~60%). Conversely, ITO offers high transmittance (>90%), but also high p-GaN contact resistance. In practice a thin inter-layer (such Ni/ NiO/ Ni/Au (annealed)) is often inserted between a transparent conducting oxide (TCO) (typically ITO) and the p-GaN to achieve both high transmittance and low contact resistance. However, indium is a limited and strategic resource and so an alternative is required. Al-doped ZnO (AZO) is a promising substitute because its properties as a transparent contact on p-GaN are similar to those of ITO. In the work, green GaN-based LEDs were fabricated from commercial epitaxy. Thin inter-layers (1-2 nm thick Ni or Ag) were deposited by electron beam evaporation. AZO (460nm) was then deposited by low temperature sputtering on to the samples, including one sample where the AZO was deposited directly on to the p-GaN layer. A control sample with a Ni/Au (5nm/5nm) was also fabricated. Results show that the inclusion of a metallic inter-layer causes a decrease in the turn on voltage and a lowering of the contact resistance, when compared with AZO only, with Ni having the most significant effect. Results will be presented of measurements of the contact resistance between AZO and p-GaN and of the effect of Ni and Ag interlayers on the contact resistance, sheet resistance and transmittance of the AZO. The effect of these inter-layers on the light output and IV characteristics of lateral LEDs will also be presented in order to develop a full understanding of the mechanisms involved in improving the contact resistance for technology optimisation.

Authors : M.Nistor 1, W.Seiler 2, C.Hebert 3,4, J.Perrière 3,4
Affiliations : 1National Institute for Lasers, Plasma and Radiation Physics (NILPRP), L22, P.O. Box MG-36, 77125 Bucharest-Magurele, Romania; 2PIMM, UMR CNRS 8006 Arts et Métiers ParisTech, 151 Boulevard de l’Hopital, 75013 Paris, France; 3Sorbonne Universités, UPMC Univ Paris 06, UMR 7588, INSP, F-75005, Paris, France; 4CNRS, UMR 7588, INSP, F-75005, Paris, France;

Resume : The understanding of the pertinent factors tailoring the electronic transport and optical properties in In2O3 [1] could be an approach to find the suitable replacement of it by indium-free oxides. Transparent In2O3 thin films were grown by pulsed electron beam deposition method on c-cut sapphire substrates at 10-2 mbar oxygen and temperature up to 500 °C, leading to the formation of dense, smooth and stoichiometric films. In2O3 cubic phase is observed even for room temperature growth, while increasing temperatures lead to a better crystallinity, epitaxial thin films being obtained at substrate temperatures higher than 200º C. Pole figure measurements indicate the existence of (111) oriented In2O3 crystallites with different in-plane symmetry, i.e. three-fold and six-fold symmetry depending upon the growth conditions. For T≤300 °C the epitaxial growth of (111) In2O3 on c-cut sapphire substrate corresponds to a “hexagon on hexagon” growth, while at higher temperatures the epitaxial relationship corresponds to a rotation of the In2O3 hexagon with respect to the sapphire hexagon. The origin of this effect is related to the specificities of the growth method which can induce a large disorder in the oxygen network of In2O3, leading to a six-fold symmetry in the (111) plane of the bixbyite structure [2], i.e. a “disordered bixbyite” phase while the “ordered bixbyite” phase presents a three-fold symmetry for the (111) plane. The behavior of the temperature dependent resistivity curves depends upon the precise oxygen composition of the films. At 200ºC the resistivity shows metallic conductivity at room temperature and a metal-semiconductor transition at low temperature, while the classical semiconductor behavior is observed for the films grown at 400 and 500ºC. A mobility of 24.7 cm2/Vs was measured at 200º C and then it falls off with improving the crystalline quality of films. The optical transparency is high (>80%) in the visible spectral range for all films, while that in the near-infrared range depends on the carrier concentration. [1] S. Lany, A. Zakutayev, T.O. Mason, J.F. Wager, K.R. Poppelmeier, J.D. Perkins, J.J. Berry, D.S. Ginley, A. Zunger, Phys. Rev. Lett. 108 016802-5 (2012) [2] W.Seiler, M.Nistor, C.Hebert, J.Perrière, Solar Energy Materials&Solar Cells 116 34-42 (2013)

Authors : Eon Ju Lee, Hyun Gyu Han, Si Ok Ryu*
Affiliations : Yeungnam University

Resume : In recent, the solution-based chemical deposition processes have been employed to deposit the insulators and the semiconductors in the fabrication of TFTs instead of the vacuum processes. Alternative high-k materials to replace SiO2, which are currently used as an insulating layer of TFT devices, are Al2O3, HfO2, ZrO2, and TiO2. Among them, Al2O3 is one of the most attractive candidates suitable to the solution-based processes because of its cheaper price and simpler process. In this study, dielectric layers and semiconductor layers were prepared by a spin coating process and an inkjet printer, respectively. For the dielectric layers, Al2O3 was deposited by the spin coating with a mixed solution of acetonitrile and ethylene glycol at room temperature. In the multi-layer coating process, the precursors trapped between the layers caused tiny pin holes in the films and they leaded to the defects on the dielectric properties. The solubility and viscosity of the precursor solution were considered in the processes. For the semiconductor layers, In2O3 were deposited by the inkjet printing. The as-deposited layers were annealed in a box furnace. The electrodes were deposited by a E-beam evaporator. Metal insulator metal device was employed to obtain the electrical properties. Physical properties of the films were investigated by SEM and AFM. The electrical characteristics of the prepared TFTs were obtained by a three-probe station.

Authors : Lukman Nulhakim1, Seichi Kishimito2, Junichi Nomoto3, Tetsuya Yamamoto3, and Hisao Makino1,3
Affiliations : 1 Graduate School of Engineering, Kochi University of Technology, Kochi, Japan 2 National Institute of Technology, Kochi College, Nankoku, Japan   3 Research Institute, Kochi University of Technology, Kochi, Japan

Resume : In this study, we investigated influences of grain size and c-axis orientation on sensitivity of hydrogen gas sensors utilizing heavily Ga-doped ZnO (GZO) thin films as sensing material. GZO films with film thickness of 30 and 100 nm were deposited by RF magnetron sputtering on glass substrate at 200 °C. Structural properties of the films were characterized by XRD measurement. The 100 nm thick GZO film showed better c-axis orientation with larger grain size compared to the 30 nm thick film that showed poor c-axis orientation and smaller grain size. Gas sensitivity was evaluated using custom made gas sensing measurement system under operating temperature of 330 °C. We found that the 30 nm thick film showed higher sensitivity compared to the 100 nm thick film. From these results, one can expect that smaller grain size or poor c-axis orientation might lead to high sensitivity. In order to clarify this issue, we deposited 30 nm thick-GZO films on highly oriented ZnO template with different thickness. The c-axis orientation of these films were nearly comparable each other, while the grain size obviously increased with increasing the thickness of ZnO templates. The sensitivity of the GZO films on ZnO template slightly increased with decreasing the grain size, and it was comparable with that of the 100 nm thick film on glass. It is more likely that c-axis orientation plays an important role on the gas sensitivity.

Authors : S. Prucnal1, M. Braun1, M. Wang1, F. Liu1, D. Snigurenko2, Y. Berencen1, E. Guziewicz2, L. Rebohle1, S. Zhou1 and W. Skorupa1
Affiliations : 1 Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, Germany 2 Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46 PL-02-668 Warsaw, Poland

Resume : A highly doped n-type ZnO thin layer is an attractive candidate to replace the much more expensive indium-tin-oxide layer in photovoltaics and low cost electronics. The optoelectronic properties of ZnO are determined by the type of doping and carrier concentration. The n-type conductivity of ZnO is easily achieved by substitution of Zn through the group III elements (Al, Ga, In), or by doping with halogen elements (F, Cl or I) substituting into the oxygen lattice site. However, the effective p-type doping of ZnO remains challenging. The most promising p-type dopants in ZnO are group V elements. In this paper, we have investigated the influence of millisecond range flash lamp annealing (FLA) on the recrystallization mechanism and optoelectronic properties of ion implanted ZnO thin films. The 120 nm thick ZnO films were grown on Si substrates by atomic layer deposition and implanted with P and Sb ions. After ion implantation FLA was used to anneal defects created during the ion implantation process and to activate finally the dopants. Samples were annealed for 3 or 20 ms using oxygen-poor (N2 or Ar) and pure oxygen atmosphere. The influence of the annealing conditions (atmosphere, annealing time and flash energy) on the optical and electrical properties of implanted ZnO was investigated using temperature dependent photoluminescence, Raman spectroscopy and Hall Effect measurements. The microstructural properties of fabricated ZnO films were studied using cross-section TEM and X-ray diffraction spectroscopy. It will be demonstrated that via millisecond range FLA treatment not only the implanted ions can be efficiently incorporated into the lattice of ZnO but also defect engineering is possible. By a proper selection of the implanted species and annealing atmosphere the main optical emission observed from doped ZnO can be easily changed from the UV to the red. This allows the fabrication of spectrally-clean blue, green and red emitters. According to Hall Effect and PL measurements the annealing atmosphere during FLA is crucial for the realization of p-type ZnO layers. The oxygen-poor atmosphere promotes the Zn-interstitial formation enhancing the n-type conductivity of ZnO. Annealing in oxygen suppresses the formation of n-type defects and stabilizes the p-type conductivity of ZnO films. This work has been partially supported by the EU 7th Framework Programme ?EAgLE? (REGPOT-CT-2013-316014).

Authors : E.Chikoidze [a], Y. Dumont [a], T. T. Huynh [b], L. L. C. Lem [b], M. R. Phillips [b], C. Ton-That [b], D. J. Rogers [c], F. H. Teherani [c], V. E. Sandana [c], P. Bove [c], R. McClintock [d], M. Razeghi [d],
Affiliations : [a] Groupe d’Etude de la Matière Condensée (GEMaC), Université de Versailles St Quentin en Y. – CNRS, Université Paris-Saclay, Versailles, France ; [b] School of Mathematical and Physical Science, University of Technology Sydney, Broadway, PO Box 123, NSW 2007, Australia ; [c] Nanovation, 8 route de Chevreuse, 78117 Chateaufort, France ; [d] Center for Quantum Devices, ECE Department, Northwestern University, Evanston, IL60208, USA ;

Resume : Conventional transparent conductive oxides (TCO) such as ITO and AZO are opaque in the UVB and UVC spectral ranges, due to their relatively small energy band gap <3.5 eV, and new TCO materials need to be explored for this purpose [1]. One such material is Ga2O3. With an optical bandgap of 4.8-5 eV it has attracted strong interest for various applications including transparent electrodes, thin film transistors, UVC sensors and LEDs [2-4]. Our work is dedicated to Ga2O3 , in the beta-phase, which is one of the five known phases and is recognised as being one of the most stable [5]. Nominally undoped beta-Ga2O3 thin films were deposited on sapphire substrates (of various orientations) using Pulsed Laser Deposition in molecular oxygen with a KrF excimer laser and a commercial 5N sintered Ga2O3 target. Highly (-201) oriented beta-Ga2O3 layers were obtained on c-, a- and r-plane sapphire. Optical transmission studies revealed high transparency (>80%) from the NIR right through to the UVC region of the spectrum and bandgaps of between 5.0 and 5.5 eV. Cathodoluminescence (CL) revealed a broad UV band peaked at 3.8 eV at room temperature. A second blue luminescence peak emerged at 3.0 eV in CL spectra acquired at 80 K. Both insulating and conductive layers were obtained by varying the growth temperature and oxygen partial pressure. In this paper we investigate the origin of these electrical transport variations through structural studies combined with temperature-dependent optical and electrical measurements. Relationships between the luminescence bands and the electrical conductivity will be discussed. 1. M. Orita, H. Ohta, M. Hirano, and H. Hosono: Appl. Phys. Lett. 77 (2000) 4166. 2. N. Suzuki, S. Ohira, M. Tanaka, T. Sugawara, K. Nakajima, and T. Shishido: Phys. Status Solidi C 4 (2007) 2310. 3. K. Matsuzaki, H. Yanagi, T. Kamiya, H. Hiramatsu, K. Nomura, M. K. Matsuzaki, H. Yanagi, T. Kamiya, H. Hiramatsu, K. Nomura, M. Hirano, and H. Hosono: Appl. Phys. Lett. 88 (2006) 092106 4. T. Oshima, T. Okuno, and S. Fujita: Jpn. J. Appl. Phys. 46 (2007) 7217. 5. R. Roy, V. G. Hill, and E. F. Osborn: J. Am. Chem. Soc. 74 (1952) 719.

Authors : R. Schifano1, A. Wierzbicka1, D. Snigurenko1, T. A. Krajewski1, D. Jarosz1, G. Luka1, K. Kopalko1, K. Goscinski1, E. Guziewicz1
Affiliations : 1Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland

Resume : ZnO has recently attracted a lot of interest as a potential semiconducting material for modern electronics. From application point of view electrical characterization of the films used in the device realization, for example using Schottky diodes (SCs), represent a key analysis, however most of the presented results concern bulk ZnO so far. With the aim of construct SCs vertical structures involving a (ZnO:Al/ZnO) bilayer (with ~100/~700 nm nominal thickness) deposited on Al2O3, GaN and ZnO by atomic layer deposition have been investigated by atomic force microscopy and X-ray diffraction and compared with the identical ones without ZnO:Al. It is shown that the presence of the ZnO:Al layer has a substantial effect on the morphology and roughness limiting the influence of the underlying substrate (RMS roughness ~10 nm independent of the substrate) as well as enlarging the FWHM of the main 00.2 reflection. Samples including the ZnO:Al layer have been annealed at 400°C in O2 to increase the resistivity from ~10-2 Ω cm to 1-10 Ω cm suitable for SCs realization. The resulting SCs revealed a rectification ratio >/~ 3 orders of magnitude in the -2 +2 voltage range. The work was supported by the Polish NCBiR project DZP/PBSII/1699/2013. Authors T.A.K. and K.G. acknowledge support by the grant DEC 2013/09/D/ST5/03879 of NSC of Poland. The author R.S. was supported by the EU 7th Framework Programme project REGPOT-CT-2013-316014 (EAgLE).

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On Device Applications of Transparent Oxide Semiconductors : CHERNS David
Authors : D. Cherns
Affiliations : School of Physics, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK

Resume : In recent years we have grown arrays of ZnO, TiO2 and InGaN nanorods for solar cell and water splitting applications. Transmission electron microscopy (TEM), carried out in cross-section (perpendicular to the growth direction) and in plan-view (along the growth axis), has led to a detailed understanding of structure and growth. Studies of (0001) InGaN nanorods grown by MBE, of interest as absorbers in solar cells and water splitting applications, show core-shell structures with a low In-content shell surrounding a high In core. Atomic resolution imaging and microanalysis reveal that both core and shell are further separated into In-rich and In-poor platelets which alternate over periods of a few nanometers, while diffraction studies show local strains of several percent which are accommodated elastically. Arrays of ZnO and TiO2 nanostructures have been investigated for use as solar cell electrodes, and TEM has been used to understand their growth and the structure of the interface with absorber and sensitiser layers. For example, studies of chemically deposited ZnS sensitiser layers on single crystal (0001) ZnO nanorods, show non-uniform growth, proceeding first on the polar (0001) surface, and by island nucleation on the non-polar facet intersections and surface steps, such that comparatively thick films are needed to form continuous layers. The paper will illustrate some of these results and show how they provide insight into the resulting optical and device properties

Authors : Nicholas Cavallari, Greta Rosa, Alessio Bosio, Roberto Fornari, Edmondo Gilioli, Francesco Pattini, Matteo Bronzoni, Filippo Annoni, Stefano Rampino
Affiliations : Nicholas Cavallari 1,2; Greta Rosa 1; Alessio Bosio 1; Roberto Fornari 1; Edmondo Gilioli 2; Francesco Pattini 2; Matteo Bronzoni 2; Filippo Annoni 2; Stefano Rampino 2 1 Department of Physics and Earth Sciences, University of Parma, Parco Area delle Scienze 7/A, 43124 - Parma, Italy, Phone: 39-0521-905222; 2 IMEM, Parco Area delle Scienze 37/A, 43124 - Parma, Italy - Phone: 39-0521-26911;

Resume : We report on fabrication and characterization of Cu(In,Ga)Se2(CIGS)–based thin film solar cell using transparent conductive oxide(TCO) as back contact. Different TCOs were investigated: ZnO:Al(AZO), SnO2:F(FTO) and In2O3:Sn(ITO), with particular emphasis on AZO and FTO being In-free. Electrical characterization of FTO and ITO revealed a carrier concentration >5•1020 cm-3 and a sheet resistance lower than 7 Ω/square, which we assumed as reference for optimizing CIGS–based devices on AZO. We found out that the Al fraction in AZO must be at least 5% in order to achieve such high carrier concentration: films deposited via Pulsed Electron Deposition using a ZnO:Al 5%wt target showed an average carrier density of 5.5•1020 cm-3 and a sheet resistance of 5 Ω/square for a thickness of about 1 micron. Preliminary results show efficiencies of 11.7% (front) and 1.6 (rear) using ITO and of 14.7% (front) and 3% (rear) using FTO for CIGS–based devices. Although efficiencies using AZO as back contact are somewhat lower, we managed to obtain preliminary values of 9.3% (front) and 5% (rear) which are higher than any other results reported in literature. Therefore, our low temperature deposition process for CIGS(250°C) seems to inhibit the formation of unwanted Ga2O3 at the interface between CIGS and back-AZO as already reported in previous works. In addition, we investigated the effects of using different dopants in ZnO, Gallium and Indium, and their impact on CIGS–based devices’ efficiencies.

Authors : R. Schifano1*, R. Pietruszka1, T. K. Krajewski1, B. S. Witkowski1, K. Kopalko1, L. Wachnicki1, E. Zielony2, K. Gwozdz2, P. Bieganski2, E. Placzek-Popko2, M. Godlewski1,3
Affiliations : 1 Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland 2 Department of Quantum Technologies, Faculty of Fundamental Problems of Technology Wrocław University of Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland 3 Dept. of Mathematics and Natural Sciences College of Science Cardinal S. Wyszynski University, ul. Dewajtis 5, 01-815 Warsaw, Poland

Resume : Numerical calculations indicate that reducing the conduction band offset (∆Ec) appearing in n-ZnO/p-Si heterojunction solar cells strongly reduces the impact of recombination centers at the interface between the two semiconducting materials, thus enabling high efficiency solar cells. By introducing Mg to reduce the band offset we have experimentally shown that there is a clear relation between higher efficiency n-ZnO/p-Si based heterojunction solar cells and lower ∆Ec (with Mg varying in the 0-4 at.%). In detail, by decreasing ∆Ec from ~0.63 eV to ~0.48 eV a corresponding rise in the solar cell efficiency from ~3.7% to ~6.0% has been observed if the ideality factor, n, is below ~2. A further ~1.1% efficiency raise is obtained by increasing the deposition temperature to 300 oC from 160 oC with approximately the same Mg content. Finally a ~10 % efficiency has been obtained on a solar cell including an anti-reflecting coating by introducing an HF pretreatment step. The increase appeared to be related to a larger VOC (~ 480 mV) pointing to an additional interfacial improvement. Acknowledgments. This work was partially supported by the National Science Centre (dec. No. DEC-2012/D6/A/ST7/00398). The author T. A. K. acknowledge support by the grant DEC 2013/09/D/ST5/03879 of NSC of Poland. The author R.S. was supported by the EU 7th Framework Programme project REGPOT-CT-2013-316014 (EAgLE).

Authors : Moritz Eyer, Sergey Sadofev, Joachim Puls, Norbert Koch, Johannes Frisch, Emil List- Kratochvil and Sylke Blumstengel
Affiliations : Moritz Eyer, Sergey Sadofev and Joachim Puls, Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12479 Berlin Norbert Koch, Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, Newtonstr. 15, 12479 Berlin Johannes Frisch, Emil List-Kratochvil and Sylke Blumstengel, Institut für Physik, Institut für Chemie & IRIS Adlershof, Humboldt-Universität zu Berlin, Newtonstr. 15, 12479 Berlin

Resume : Hybrid structures of organic semiconductors and transparent conductive oxides (TCO) offer wide possibilities for new opto-electronic devices as they can take advantage of different functionalities of the inorganic and the organic components. For example, in hybrid photovoltaics the high carrier mobility of TCOs can be combined with the high absorption coefficient of organic conjugated molecules. The performance of hybrid photovoltaic devices is determined by the efficiency of the charge separation process. Excitons generated in the organic and inorganic part diffuse to the interface of the heterojunction and dissociate. Our experiments show that prior generation of free charge carriers, a hybrid charge transfer exciton (HCTE) is formed, i.e. a coulombically bound charge pair residing on both sides of the interface. Only after dissociation of such a pair a photocurrent is generated. The formation of HCTE and their properties are elucidated in planar ZnMgO/poly(3-hexylthiophene) (P3HT) heterojunction devices by photoemission spectroscopy, electroluminescence (EL), photovoltaic EQE and I-V measurements. The energy offset ΔE_io between the conduction band minimum of ZnMgO and the P3HT highest unoccupied molecular orbital is systematically tuned by varying the Mg content. Both, the HCTE EL transition energy and the open circuit voltage V_OC scale linearly with ΔE_io indicating the correlation of both quantities. The photovoltaic performance is thus closely interlinked with the properties of the HCTE. Combined analysis of HCTE EL and photovoltaic performance provides thus valuable input for the optimization of interfaces between TCOs and organic semiconductors to fully exploit the potential of hybrid devices.

Authors : Sofie Bitter, Peter Schlupp, Holger von Wenckstern, Marius Grundmann
Affiliations : Universität Leipzig, Institut für Exp. Physik II, Germany

Resume : Amorphous zinc-tin-oxide (ZTO) consists of naturally abundant, nontoxic elements only and can be deposited at room temperature with an electron density and a mobility as high as 10^19 cm^-3 and 10 cm^2/Vs, respectively [1]. Therefore, ZTO is a suitable material for low-cost, transparent transistors and generally low-cost, transparent electronic applications. We present our results on the influence of the Zn/Sn ratio on the electrical properties of thin films grown by pulsed laser deposition on glass substrates using a continuous composition spread method [2]. Amending previous reports on only a limited number of discrete Zn/Sn ratios [3], we obtained a comprehensive data set for almost the entire composition range. Using energy dispersive X-ray analysis the spatial dependence of the Zn/Sn ratio was mapped. Charge carrier concentration and resistivity were determined in dependence on the composition [4]. Further, the properties of all-amorphous pn-heterojunctions using zinc-cobalt-oxide (ZCO) as p-type electrode will be discussed in dependence on the thin film stoichiometry. An improvement of the diode characteristics regarding the ideality factor and the rectification ratio is observed with aging. [1] Jayaraj et al., J. Vac. Sci. & Technol. B, 26, 2 (2008) [2] von Wenckstern et al., CrystEngComm, 15, 10020 (2013) [3] Görrn et al., Applied Physics Letters, 91, 193504 (2007) [4] Bitter et al., ACS Comb. Sci., 18, 188 (2016)

Authors : L. Farrell, E. Norton, C. M. Smith, D. Caffrey, I. V. Shvets, K. Fleischer
Affiliations : School of Physics and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), Trinity College, The University of Dublin, Dublin 2, Ireland

Resume : The material system of CuCrO2, a delafossite, is well known as one of the best performing p-type transparent conducting oxides. We report details on a low temperature facile growth method for CuCrO2 by spray pyrolysis. The dependence of the growth on the precursors, the temperature and oxygen partial pressure is examined. The decomposition routes are critical to obtain the best performing films. The thermopower and electrical measurements indicate p-type films with conductivity ranging from 1-12 Scm?1 depending on the growth conditions. This p-type conductivity is retained despite the nanocrystallinity of the films. The figure of merit of these films can be as high as 350 ?S, which is the best performing p-type TCO by solution methods to date. Comprehensive analysis of the thin films by X-Ray Diffraction, Raman spectroscopy, X-ray absorption spectroscopy and X-ray photoelectron spectroscopy was used to identify the material as a highly Copper deficient CuxCrO2, with best performance in terms of the figure of merit found for x=0.4. Interestingly, the material?s low growth temperature is compatible with flexible substrates, glass (Corning Willow® glass) and plastic sheets (Kapton® polyimide). We discuss the optical and electrical properties and morphology of films grown on variety of glass and flexible substrates as well as their bending stability.

On ZnO and related materials 1: Deposition Technologies and Materials properties: : -
Authors : C. Frijters, W.H.P van Boekel, P.J. Bolt, B.S.P. de Raadt, P. Poodt, A. Illiberi
Affiliations : Solliance/TNO, Eindhoven, 5656AE, The Netherlands

Resume : Spatial ALD is emerging as an industrially scalable deposition technique at atmospheric pressure which combines the advantages of temporal ALD, i.e. excellent control of film composition and uniformity on large area substrates, with high growth rates (up to nm/s). We present the S-ALD of indium-free transparent conductive oxides (TCOs): ZnO, ZnSnO and Al:ZnO. Temporal ALD of multicomponent oxides is carried out by alternating the growth of different binary oxides, so that the film composition and morphology changes along the growth direction. This results typically in a low carrier mobility and poor doping efficiency in Zn-based TCOs. In S-ALD a moving substrate is sequentially exposed to the oxygen precursor and metal precursor vapors (i.e. DEZ, TDMA-Sn, TMAl, DMAI), which are pre-mixed and co-injected in the same deposition zone. The successful application and the limitations of this new method will be presented for different precursors. A much higher doping efficiency of Al-atoms (~ 90 %) is achieved in ZnO:Al when DMAI, instead of TMA, is co-injected with DEZ. A minimum resistivity of 0.5 mOhm cm and an optical transparency of ~ 90 % in the visible range are measured in 750 nm thick Al:ZnO. The morphology of the ZnSnO and ZnOAl varies from polycrystalline to amorphous with increasing the dopant concentration, as measured by X-ray diffraction. The application of S-ALD indium-free transparent conductors in c-Si, CIGS solar cells and OLEDs is currently under investigation.

Authors : Elzbieta Guziewicz, Ewa Przeździecka, Dmytro Snigurenko, Dawid Jarosz, Bartlomiej S. Witkowski, and Wojciech Paszkowicz
Affiliations : Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland

Resume : The stable p-type conductivity of ZnO is still the main obstacle in a wide application of this material in optoelectronics. It has been reported that doping ZnO with group V elements results in enhancement of luminescence intensity around 3.30-3.32 eV. However, it has been shown that in epitaxial films the acceptor-related 3.31 eV luminescence comes from stacking faults [1]. We report on a photo- and cathodoluminescence on polycrystalline ZnO and ZnO:N films grown at 100^oC by Atomic Layer Deposition. Photoluminescence spectra show two emission bands in the excitonic region. Apart from the DoX line at 3.36 eV, a characteristic emission at 3.30 – 3.32 eV appears both in undoped and nitrogen-doped samples, however the RTP annealing in oxygen atmosphere leads to a considerable enhancement of this band only in samples intentionally doped with nitrogen. This enhancement is accompanied by shifting the conductivity towards p-type. Spatially resolved low-temperature cross-section CL studies show that the area showing donor-related 3.36 eV emission is complementary to the area showing acceptor-related ~3.3 eV band, which suggests that both p-type and n-type regions simultaneously coexist in this material. This points out that the 3.31 eV band cannot be clearly associated with stacking faults as was suggested before [1]. Acknowledgements. The work was partially supported by the Polish NCN project DEC-2012/07/B/ST3/03567. References [1] M. Schirra et al., Phys. Rev. B77, 125215 (2008).

Authors : S. Fabert, R. Meunier, M. Carette, P-Y. Thoulon, M. Ricci, A. Goullet, P-Y. Jouan, M-P. Besland
Affiliations : Institut des Matériaux Jean Rouxel (IMN) UMR CNRS 6502 44322 Nantes ; Crosslux S.A. Avenue Georges Vacher 13790 Rousset ; Institut d'Electronique de Microélectronique et de Nanotechnologie (IEMN) UMR CNRS 8520 59652 Villeneuve d'Ascq

Resume : Among transparent conductive materials (usually known as TCOs), Zn(O,S) represents an attractive alternative to ITO or other doped ZnO. The objective stands in finding the best compromise between good conductive properties and high transparency. Published works on ZnO:S thin films have widely shown how the targeted TCO properties are strongly dependant on the oxygen content [1][2]. In this study, the deposition of Zn(O,S) thin films were performed by radiofrequency magnetron sputtering in reactive Ar-O2 plasma, starting from two different ZnS targets, with oxygen atomic content in the 10% and 30% range. The properties of Zn(O,S) layers, i.e. chemical, structural, morphological and optical properties, have been investigated by XPS, XRD, SEM, TEM, ellipsometry and UV-visible spectrometry. In our presentation, we will illustrate how the target composition modifies the process characteristics and the layers properties. Finally, we will focus on process characteristics allowing to reach the best TCO properties in ZnO:S films. [1] B-K. Meyer et al, Applied Physics Letters vol. 85 4929-4931(2004) [2] G. Baldissera and C. Persson, Journal of Applied Physics, vol 119, 045704 (2016)

Authors : John Buckeridge, C. R. A. Catlow; T. W. Keal; A. J. Logsdail, D. O. Scanlon; P. Sherwood; A. A. Sokol, S. M. Woodley; A. Walsh
Affiliations : University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, United Kingdom; Scientific Computing Department, STFC, Daresbury Laboratory, Daresbury, Warrington WA4 4AD, United Kingdom; University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, United Kingdom; Scientific Computing Department, STFC, Daresbury Laboratory, Daresbury, Warrington WA4 4AD, United Kingdom; University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, United Kingdom; Centre for Sustainable Chemical Technologies and Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom

Resume : The formation of oxygen vacancies and their effect on the n-type conductivity of transparent conducting oxides (TCOs) has remained a controversial topic. They have been determined to be deep donors in SnO2 and ZnO, while it has been proposed that their formation on the surface of In2O3 would lead to intrinsic n-type conduction. Numerous computational studies on this subject have tried to correlate the calculated defect properties with available experimental spectroscopic data (luminescence etc.), but, notably, often contradicting each other in the defect assignment. We use state-of-the-art hybrid quantum mechanical/molecular mechanical solid state embedding to determine the formation energy, electronic and optical properties of the oxygen vacancy in the three archetypal TCOs In2O3, ZnO and SnO2. To ensure a high level of accuracy in our simulations, we employ three hybrid exchange and correlation density functionals (PBE0, B97-2 and BB1k) and compare their predictions with previous plane-wave pseudopotential based calculations and experiment. Our results using the PBE0 functional are in excellent agreement with calculations done using a plane-wave basis set, which predict the oxygen vacancy to be a deep donor in all three systems. Using BB1k, which has been developed specifically to treat both reaction energies and kinetic barriers accurately, we find, in contrast to previous studies, that the oxygen vacancy is a resonant shallow donor in bulk In2O3. In SnO2 and ZnO we show that the vacancy is indeed a deep donor, but shallower than previously proposed. Our results are in excellent agreement with available deep level transient spectroscopy measurements and other relevant experimental data.

Authors : Shuqun Chen, Russell Binions
Affiliations : School of Engineering and Materials Science Queen Mary University of London

Resume : Zinc oxide thin films were deposited from the aerosol assisted chemical vapour deposition reaction of zinc acetate dihydrate in methanol on to glass substrates. The addition of acetic acid and / or water into the reaction flask led to large changes in the films microstructure, texturing and roughness. By careful tailoring of the reaction mixture columnar, hexagonal pyramid or hexagonal plate structures could be deposited. the changes in structure led to large changes in both optical and electrical properties of the films, specifically an increase in haze (up to 95%) or a decrease in film resistance (60 ohm.sq-1). Aerosol assisted chemical vapour deposition shows great promise as a simple and flexible method to produce high quality zinc oxide thin films.

On ZnO and related materials 2: Device Related Materials Properties : APOSTOLUK Alexandra
Authors : A. Apostoluk1, Y. Zhu1, B. Masenelli1, A. Valette2, P. Gautier2, N. Le Bail2,3, S. Daniele2, V. Consonni4, E. Appert4, R. Parize4, J.-J. Delaunay5, K. Znajdek6, M. Sibinski6
Affiliations : A. Apostoluk1; Y. Zhu1; B. Masenelli1 1 Université de Lyon Lyon Institute of Nanotechnology (INL, UMR CNRS 5270), Lyon Institute of Applied Sciences (INSA Lyon) 7 Avenue Jean Capelle, 69621 Villeurbanne, France A. Valette2; P. Gautier2; N. Le Bail2,3; S. Daniele2 2 Université de Lyon Institut de Recherches sur la Catalyse et l’Environnement de Lyon (IRCELYON), UMR CNRS 5256, Université Claude Bernard Lyon 1, 2 Av. Albert Einstein, 69626 Villeurbanne, France 3 Lotus Synthesis SAS, F-69100 Villeurbanne, France V. Consonni4; E. Appert4; R. Parize4 4 Laboratoire des Matériaux et du Génie Physique (LMGP), UMR CNRS 5628, Grenoble INP-Minatec, 3 Parvis Louis Néel, CS 50257, 38016 Grenoble, France J.-J. Delaunay5 5 The University of Tokyo, School of Engineering, Department of Mechanical Engineering, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan K. Znajdek6; M. Sibinski6 6 Łódź University of Technology, Department of Semiconductor and Optoelectronics Devices (DSOD), ul. Wolczanska 211/215, 90-924 Łódź, Poland

Resume : Most of the existing photovoltaic (PV) solar cells are already optimized in terms of their absorption and conversion efficiency, however any strategy that can help to raise their efficiency, even slightly, is welcome, and all the more if it is cheap and does not require any modification of the solar cell fabrication technology. One possibility to increase solar cell’s efficiency is the use of a material that could convert the high energy photons from the sun spectrum, namely UV and blue light, which are otherwise inefficiently absorbed by the amorphous Si, CdTe, CIGS and organic PV cells, and re-emit them as lower energy photons, for which the conversion efficiency of these cells is optimal. This so-called “down-shifting” strategy belongs to the “add-on” technology, as the aim is to fabricate a thin layer of the down-shifting material on top of the existing solar cells and all this at low cost. The criteria which a good down-shifting material needs to fulfill are: having a large Stoke shift (i.e. a discrepancy between the absorption and emission energies) and possessing high photoluminescence quantum yield (PL QY). Furthermore, this material has to be environmental-friendly and cheap. Several attempts were reported in the literature aiming at the fabrication of such a material. For example, CdS and CdSe nanoparticles embedded in polymers or silica have proved to be efficient but not necessarily cheap and non-toxic. However, high PL QY, stable green/yellow emission and easy scale–up process are expected for industrial applications. We study down-shifting materials based on ZnO nanoparticles. ZnO is a low cost, abundant and non-toxic material. It naturally absorbs the blue and UV light thanks to a wide band gap of about 3.37 eV at room temperature. ZnO can also emit visible light, from yellow to red, depending on the nature of the crystalline and surface defects involved in the emission process. Although the nature of these defects is still under debate, it is widely admitted that reducing the size down to the nanoscale enhances the presence of the defects and the luminescence efficiency of ZnO nanostructures in the visible. We present a quick and convenient chemical solution approach to get unique mesospheric self-assembly hybrid ZnO system with intense photoluminescent quantum yield of 40-75 % and stable visible emissions. We develop luminescent layers of ZnO nanoparticles dispersed and embedded in a polymer matrix to be used as down-shifting materials in the structures of solar cells. Our luminescent ZnO layers are fabricated using an easy scale–up process, which is easily adaptable for industrial applications. We will also present the parameters influencing the luminescent efficiency of chemically synthesized ZnO nanoparticles used as down-shifting material. The issue of the optimization of the luminescence EQE, in conjunction with the nano- and mesostructure of the material will also be addressed. We will show how the chemical synthesis parameters influence the ZnO nanoparticle’s EQE and how they can be adjusted to reach EQE as high as 75 %. The possibility to disperse and embed the nanoparticles in polymers (for example PMMA) will also be discussed. Furthermore, the possibility of application of other ZnO nanostructures, namely zinc oxide nanowires, in gas sensors, is presented. These nanowires are fabricated by a simple and low-cost process - chemical bath deposition. They have similar luminescent properties as studied ZnO nanoparticles, i.e. they emit in the UV and in the visible spectral range, thanks to the defects and surface states. Their excitonic and visible emission is studied in the presence of gas vapors and the results demonstrate the change of the visible photoluminescence of ZnO nanowire array and that the material is able to adsorb gases. Finally, the mechanism of gas sensing is discussed.

Authors : M. K. Hamza,a K. Masenelli-Varlot,b M. Bugnet,b B. Canut,a O. Boisron,c P. Melinon,c B. Masenellia
Affiliations : a: Institut des Nanotechnologies de Lyon, INSA-Lyon, UMR CNRS 5270, Université de Lyon, 7 avenue Jean Capelle, 69621 Villeurbanne Cedex, France. E-mail: b: Université de Lyon, INSA-Lyon, MATEIS UMR CNRS 5510, 7 avenue Jean Capelle, 69621 Villeurbanne Cedex, France c: Institut Lumière Matière, Université Lyon 1, UMR CNRS 5306, Université de Lyon, 69622 Villeurbanne cedex, France

Resume : Transparent oxide semiconductors nanostructures are promising systems to expand the significant achievements of plasmonics into the infrared (IR) range [1,2]. We report on tunable mid IR plasmon induced in degenerate Al and Ga doped ZnO nanostructures considering their wide range of possible doping levels and thus of plasmon tuning.4 The plasmon resonances of nanocrystal(s) and nanowires can clearly be tuned between 2000 cm-1 and 3000 cm-1 by introducing donor dopants. We thus investigate the reasons for this large damping and identify two distinct mechanisms. We first show that by embedding the GZO nanocrystals in Al2O3 matrix has prevented the OA, and hence the damping was reduced along with the broadening. The second mechanism is related to the partial activation of the dopants. The partial activation is the consequence of two causes. First, depending on the synthesis conditions, acceptors defects can be created among the nanoparticles or nanowires and compensate the intentionally introduced donors. We have shown that the activation of Al is enhanced when it is introduced in ZnO nanocrystals synthesized in O-poor conditions rather than in O-rich conditions [3]. In this case, acceptors complexes related to O vacancies are minimized. The second reason is partial activation of the dopants. We have observed that less than half of the dopants actually participate to the electron gas. The cause of the partial activation is related to the position of the dopants within the particles. It has been proposed that if the dopants are homogeneously distributed the damping is larger . Via STEM EELS, we map the spatial distribution of dopants within the nanocrystals at the atomic scale. We subsequently anneal the nanocrystals to let them reach the thermodynamic equilibrium and map again the distribution of dopants to see whether the latter have segregated through a self-purification process. The effect of the return to the thermodynamic equilibrium on the Plasmon resonance is concomitantly investigated. References [1] G.V. Naik, V.M. Shalaev, A. Boltasseva, “Alternative Plasmonic Materials: Beyond Gold and Silver”, Adv. Mat. 2013, 25, 3264-3294. [2] M. K. Hamza, J.-M. Bluet, K. Masenelli-Varlot, B. Canut,O. Boisron, P. Melinon and B. Masenelli.”Tunable mid IR plasmon in GZO nanocrystals”. Nanoscale, 2015, 7, 12030 [3]S. D. Lounis, E.L. Runnerstrom, A. Llordes, D. J. Milliron, “Defect chemistry and plasmon physics of colloidal metal oxide nanocrystals”, Phys. Chem. Lett.2014, 5, 1564-1574.

Authors : Sascha Kalusniak, Laura Orphal and Sergey Sadofev
Affiliations : Humboldt-Universität zu Berlin, Department of Physics, 12489 Berlin, Germany

Resume : The interaction of metals with electromagnetic radiation gives rise to collective charge excitations called surface plasmon polaritons (SPPs). The potential of these coupled light-matter states for creating nano-scale photon-based circuits is the core of what is summarized today by the term "plasmonics". We will show that strongly n-type ZnO is an excellent plasmonic material in the infrared spectral range. Using molecular beam epitaxy, we are able to generate free carrier concentrations of almost 10E21 cm-3 by Ga-doping of ZnO without significant deterioration of the crystal perfection. In this way, a metallic dielectric function is created with a negative-to-positive crossover of the real part tunable from mid infrared up to telecommunication wavelengths. The losses are at least one order of magnitude lower than for traditional metals. Fabrication of epitaxial multilayer structures with different doping level enables the formation of novel SPP dispersions that can be engineered in a unique way. Coupling of SPPs at adjacent interfaces allows for almost arbitrarily shaping of their dispersion curves for achieving, e.g., phase matching for nonlinear processes or even anomalous dispersion. Moreover, the controllable stacking of alternate subwavelength-thin metallic and dielectric layers in a multilayer structure opens a direct route for realization of hyperbolic metamaterials. We demonstrate realization of ZnO-based hyperbolic metamaterials operating at wavelengths covering the entire telecommunication band.

Authors : Emila Panda, Chetan Singh, Tvarit Patel
Affiliations : Department of Materials Science and Engineering, Indian Institute of Technology Gandhinagar, Palaj, Gandhinagar 382355, Gujarat, India

Resume : In this work detailed investigation on the surface and bulk electrical properties of the Al-doped ZnO (AZO) films fabricated under various experimental conditions in RF magnetron sputtering was carried out using Scanning Tunnelling Microscopy/Scanning Tunnelling Spectroscopy (STM/STS), Conductive Atomic Force Microscopy (C-AFM) and Hall probe measurement system. Both these properties showed substantial variation with respect to their microstructure, a consequence of the growth conditions, hence altering their surface and bulk chemistries. An increase in the carrier concentration is found to be strongly influenced by the presence of the shallow donor level defects, whereas, deep donor level defects were not found to contribute to it. The highest carrier mobility of the film is found to occur for the most oriented and larger crystallite growth. The combination of an increased concentration of the shallow donor level defects and an absence of the deep donor level defects are found to correspond with the best values of carrier concentration and carrier mobility leading the lowest electrical resistivity of 0.913×10-3 Ω-cm. The local surface conductivities and their spreads are found to be larger for the films with lower bulk electrical resistivity. Moreover, this study sheds light on the use of specific experimental tools (like, Hall probe measurement system, Photoluminescence, C-AFM and STM/STS) as an indicator to estimate the overall film quality in a stand-alone manner, hence making the extensive use of a wide range of characterization techniques for optimizing the film quality of the transparent conducting oxide (TCO) redundant.

Authors : Jens Niederhausen 1,2, Antoni Franco-Cañellas 3, Simon Erker 4, Martin Oehzelt 2, Thorsten Schultz 1, Patrick Amsalem 1, Pardeep K. Thakur 5, Katharina Broch 6, David Duncan 5, Anton Zykov 1, Stefan Kowarik 1, Tien-Lin Lee 5, Alexander Gerlach 3, Oliver T. Hofmann 4, Frank Schreiber 3, Norbert Koch 1,2
Affiliations : 1: Institut für Physik, Humboldt-Universität zu Berlin, 12489 Berlin, Germany 2: Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin, Germany 3: Institut für Angewandte Physik, Universität Tübingen, 72076 Tübingen, Germany 4: Institut für Festkörperphysik, TU Graz, 8010 Graz, Austria 5: Diamond Light Source, Harwell Science and Innovation Campus, Oxfordshire OX11 0DE, UK 6: Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Germany

Resume : The atomistic details of metal oxide surfaces control their electronic and catalytic properties. In the case of ZnO, rich phase diagrams are predicted by ab-initio calculations, with the considered structures allowing for surface reconstructions, adsorbates, and relaxation of surface-near layers. Since these characteristics are interrelated, a clear identification of a given surface structure is significantly assisted by experimental techniques that yield structural information with chemical sensitivity. In addition, such experiments help identifying important chemical species and preparation conditions that have hitherto not been considered, thus allowing to refine the computational studies. With X-ray standing waves (XSW), atomic positions can be independently resolved for the species found in an X-ray photoelectron spectrum. We collected XSW data for ZnO single crystals treated ex-situ only and investigated the effect of several in-situ treatments. By variation of temperature and H2O partial pressure we determined structures for selected points in the phase diagram. In addition, we evidenced deterioration of the surface-near crystallinity by Ar incorporation during Ar+ sputtering and studied the annealing behavior.

Authors : Kentaro Kaneko1,2, Keiichi Tsumura 2, Takeyoshi Onuma 3, Takayuki Uchida 2, Riena Jinno 2, Tomohiro Yamaguchi 3, Tohru Honda 3, and Shizuo Fujita 1,2
Affiliations : 1 Photonics and Electronics Science and Engineering Center, Kyoto University, 2 Department of Electric Science and Engineering, Kyoto University 3 Department of Applied Physics, Graduate School of Advanced Engineering, Kogakuin University

Resume : In recent years, DUV light sources using wide band gap semiconductor have been getting huge attention as an alternative of gaseous light sources for their low-cost, safety and having long product lifetime. Among wide band gap semiconductors, Mg1?xZnxO which is an alloy of magnesium oxide (MgO) and zinc oxide (ZnO) is an unexplored and promising candidate material because its bandgap can be tuned from 3.3 eV to 7.8 eV, that is, the maximum band-gap can be larger than that of AlN. However, there are few reports on DUV luminescence from Mg1?xZnxO. Almost reports are studied on wurtzite-structured Mg1?xZnxO for the band gaps smaller than about 5 eV. We focused attention on rocksalt-structured Mg1?xZnxO having wider band gaps. Mg1?xZnxO alloy films were grown on MgO (001) substrates by mist CVD method. Growth temperatures were settled at 500 - 800 C. Molar ratios of Zn source were changed from 10 to 40 % in precursor sources. In an x-ray diffraction (XRD) profile, Mg1?xZnxO and MgO 002 peaks were confirmed and other crystal phases were not detected for entire range of Zn concentartions. It was found that oriented grown Mg1?xZnxO thin films were obtained on MgO substrates at 600 and 700 C for each growth conditions of various molar ratios of Zn in source solutions. A cathodoluminescence (CL) spectra of a Mg0.64Zn0.36O thin film on a MgO substrate, DUV emission peaks were observed around 5.3 eV (234 nm) at low temperature of 11 K, though the intensity rapidly decreased with increasing temperature to 300 K. The MgO substrate was confirmed to exhibit no emission around 5.3 eV. Since the band gap of Mg0.64Zn0.36O is calculated as 6.2 eV, it may be concluded that the DUV emission at 5.3 eV is originating from a near-band-edge (NBE) emission of the Mg0.64Zn0.36O film.

On SnO2 and related materials : PEMBLE Martyn
Authors : Martyn E Pemble, Jennifer Halpin , Jan Kegel, Melissa McCarthy, Shane O'Brien, Ian M Povey, Louise Ryan, Adrian Walsh
Affiliations : Martyn E Pemble, Department of Chemistry and Tyndall National Institute, University College Cork, Cork, Ireland, Jennifer Halpin , Jan Kegel, Melissa McCarthy, Shane O'Brien, Ian M Povey, Louise Ryan, Adrian Walsh Tyndall National Institute, University College Cork, Cork, Ireland

Resume : In the first part of this presentation it will be demonstrated that Al-doped ZnO grown by atomic layer deposition (ALD) in 'nanolaminate' mode whereby the dopant Al species are introduced via an ALD cycle that interrupts the ALD growth of ZnO itself, exhibits resistivities as low as 0.002 while maintaining transparency at levels around 70%, despite the fact that the dopant atoms are effectively placed at specific points within the ZnO layer. It is suggested that this unconventional approach to dopant incorporation, which might be termed true 'delta-doping', offers a number of exciting possibilities in terms of potential applications, not the least being as the transparent conducting electrodes in perovskite-based solar cells. In the second part the potential use of Co-doped ZnO as a photoanode for the solar splitting of water will be outlined while the photocatalytic activity of this material will be demonstrated with a view to it forming the basis of simple sensor and water splitting devices. In addition we demonstrate that these materials, which are grown using a combination of ALD and hydrothermal processes, exhibit unusual optically-active defects following thermal processing which could also facilitate their use in a range of interesting new applications.

Authors : Peter Schlupp, Holger von Wenckstern, Sofie Bitter, Marius Grundmann
Affiliations : Inst. f. Exp. Physik II, Universität Leipzig, Germany

Resume : Amorphous zinc tin oxide (ZTO) can be fabricated at room temperature and exhibits electron mobilities of more than 10 cm^2/Vs [1]. This makes its use interesting for channel layers in pixel driving thin film transistors for active matrix displays. Bipolar (hetero-)diodes [2] as well as Schottky barrier diodes are viable options for switching gate electrodes for low voltage operation. They can additionally be employed for material characterization by space charge spectroscopy. We present Schottky barrier diodes on ZTO using platinum contacts. The semiconducting films are grown by pulsed laser deposition, the Schottky contacts by reactive direct current sputtering. Diodes exhibit rectification ratios of more than 5 orders of magnitude. Temperature dependent current voltage characteristics were obtained and modelled using thermionic emission model. A mean barrier heigth of about 1.3 eV is obtained for diodes with an ultrathin semi-insulating layer between semiconductor and Schottky metal. Additionally, capacitance-voltage and thermal admittance spectroscopy were performed. We found two defect levels in amorphous ZTO, one deep level at about 200 meV and one shallow level near the conduction band minimum who's properties are discussed following the method of Pautrat et al. [3]. [1] Jayaraj et al., J. Vac. Sci. Technol. B 26, 495 (2008) [2] Schlupp et al., Adv. Electron. Mater 1, 140023 (2015) [3] Pautrat et al., Solid-State Electron. 23, 1159 (1980)

Authors : Christian A. Niedermeier(1,2), Sneha Rhode(1), Lars Blumenthal(3), Keisuke Ide(2), Toshio Kamiya(2,4), Michelle A. Moram(1)
Affiliations : (1) Department of Materials, Imperial College London, Exhibition Road, London, SW7 2AZ, UK; (2) Materials and Structures Laboratory, Tokyo Institute of Technology, Mailbox R3-4, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan; (3) Department of Physics, Imperial College London, Exhibition Road, London, SW7 2AZ, UK; (4) Materials Research Center for Element Strategy, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan

Resume : Transparent oxide La:BaSnO3 demonstrates great potential as a high-mobility electron transport layer for applications in flat panel displays, solar cells, light-emitting diodes, and multi-functional perovskite-based electronic devices. While an extraordinary high room-temperature mobility of 320 cm2/Vs has been reported for La:BaSnO3 single crystals[1], epitaxial La:BaSnO3 thin films grown on SrTiO3 substrates suffer from the presence of dislocations and domain boundaries that cause electron scattering. This work presents epitaxial growth of high mobility La:BaSnO3 thin films by pulsed laser deposition (PLD) on NiO-buffered MgO substrates of less than 1.4% lattice mismatch. The maximum Hall mobility of 69 cm2/Vs is among the highest for films prepared by PLD on SrTiO3 or BaSnO3 substrates[2] and solid phase epitaxy[3]. High resolution transmission electron micrographs show a coherent La:BaSnO3/NiO interface free of dislocations that may affect the electronic transport. By variation of the carrier concentration from 8.3 × 10^18 cm-3 to 4.9 × 10^20 cm-3, the increase in the electron effective mass is evaluated from the free carrier absorption observed in Fourier transform IR spectra. The 170 meV widening of the direct optical band gap is described by an analytical model taking into account band gap narrowing by heavy doping and the non-parabolic La:BaSnO3 conduction band. From temperature-dependent electronic transport properties the prevailing carrier scattering mechanisms are discussed for design of low-defect density, high mobility epitaxial films at moderate doping levels of about 1 × 10^20 cm-3, since ionized impurity scattering limits carrier transport at all doping levels beyond. [1] H. J. Kim et al. Appl. Phys. Express 5, 061102 (2012). [2] W. J. Lee et al. Appl. Phys. Lett. 108, 082105 (2016). [3] C. A. Niedermeier et al. Appl. Phys. Lett. 108, 172101 (2016).

Authors : Toshihiro Okajima 1, Junjun Jia 2, Haruka Yamamoto 2, Yuzo Shigesato 2
Affiliations : 1 Kyushu Synchrotron Light Research Center, Tosu, Saga 841-0005, Japan. ; 2 Graduate School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo, Sagamihara 252-5258, Japan.

Resume : Rutile and anatase TiO2 films are widely used in various industrial applications [1,2]. Rutile TiO2 film is utilized as the optical coating material due to its high refractive index, and anatase TiO2 film is applied as photocatalysts and transparent electrodes. Many experimental techniques were investigated to control the crystal phase in TiO2 thin films. Impurity doping and the controlling of sputtering conditions are most useful techniques [3,4]. Recently, we revealed that Sn doping induced the transformation of TiO2 crystal structure from anatase to rutile phase [5]. In this study, we focused on the origin of rutile to anatase conversion of TiO2 thin film prepared by the sputtering process with Sn doping. We investigated the local structures of Sn ions in TiO2 thin film by X-ray absorption spectroscopy, indicating the Sn ions were substituted at Ti site in rutile TiO2 thin film. The first-principles calculations revealed that the formation energy of SnTi defect in rutile TiO2 was lower than that in anatase TiO2. We will discuss the mechanism on the effect of Sn doping on the crystal structure. [1] J. M. Bennett, et. al., Applied Optics 28, 3303 (1989), [2] Y. Furubayashi, et. al., Appl. Phys. Lett. 86, 252101 (2005), [3] S. S. Pradhan, et. al., Thin Solid Films 520,1809 (2012), [4] K. Okada, et. al., J. Am. Ceram. Soc. 84, 1591 (2001), D. Mardare, et. al., Appl. Surf. Sci. 156, 200 (2000), [5] H. Kotake, et. al., J. Vac. Sci. Technol. A 33, 041505 (2015).

Authors : Oliver Bierwagen, Zbigniew Galazka
Affiliations : Paul-Drude-Institut für Festkörperelektronik, Berlin, Germany; Leibniz Institut für Kristallzüchtung, Berlin, Germany.

Resume : The wide-band gap semiconductor SnO2 has been used for decades as polycrystalline material in gas sensors and, highly donor doped, in transparent contacts. Recent years brought a renewed interest in single crystalline semiconducting oxides for research into their basic physics, ultimate materials performance, and novel applications. This contribution benefits from unintentionally-doped rutile SnO2 bulk single crystals grown by physical vapor transport [1] to determine the impact of its anisotropic crystal structure [1,2] and effective electron mass [2] on the electron transport with direct relevance for In-free TCO and electronics applications. For this purpose van der Pauw-Hall measurements were performed with (110) and (100) oriented square shaped wafers contacted in the corners. The mobilities in a and c-direction were extracted by comparing the measurement results to finite element simulations of anisotropic transport for this geometry [3]. The extracted mobility anisotropy largely agrees with the effective mass anisotropy [2] for both, limiting phonon and impurity scattering. The increasing effective mass anisotropy with electron concentration [4] directly increases the benefits of a proper crystal(lite) orientation on electron mobility in SnO2-based TCO layers. [1] Galazka et al., Phys. Status Solidi A 211 (2014). [2] Button et al., Phys. Rev. B 4, 4539 (1971). [3] Bierwagen et al., Phys. Rev.B 70, 165307 (2004). [4] Feneberg et al., Phys. Status Solidi A 211 (2014).

Authors : Andrew Clarke, Jack Eden, Dr Howard Snelling, Dr Christopher Walton
Affiliations : University of Hull; University of Hull; University of Hull; University of Hull

Resume : Many applications of transparent conductive oxides (TCOs) would benefit from the ability to be able to deposit them as thin films at low temperatures. By removing the need for high temperature deposition techniques, the ability to use polymer substrates for flexible electronics is gained. However, low temperature methods for solution-deposited films (e.g. printed TCOs), still require high temperature, post-deposition, treatment to achieve transparency together with high conductivity. Here we demonstrate laser processing as a viable alternative to oven-based treatments. In particular, the rate of heating is explored as it is this that allows the laser-induced temperature rise to exceed the conventional upper working limit of the substrate. Thermal modelling has been carried out for laser irradiation of TCO films. Validation of these models has been achieved through the use of an IR camera recording live temperature data. Experimental laser irradiation of solution deposited TCO films has been conducted and preliminary data are presented here. The resistivity of TCO films deposited at low temperatures has been reduced with both UV and IR lasers without damaging the underlying substrate. Both photothermal and photochemical effects have been observed to improve the conductivity of the thin film. This work was conducted as part of the INFINITY project which has received funding from the European Union?s Horizon 2020 research and innovation programme under grant agreement No 641927.

Authors : E. Guziewicz 1*, P. Terziyska 2, G. Łuka 1, T. A. Krajewski 1, E. Vlakhov 2
Affiliations : 1 Institute of Physics, Polish Academy of Sciences, 32/46 al. Lotnikow, 02-668 Warsaw, Poland, 2 Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd, 1784 Sofia, Bulgaria

Resume : Zinc oxide films deposited at temperature below 200°C have been intensively investigated because they are prospective candidates for novel electronic applications such as switch elements in three-dimensional memories and inorganic partners of hybrid organic-inorganic structures. Therefore control of conductivity and optical properties of such layers is of a great interest from both scientific and application points of view. These properties are significantly different than in ZnO films obtained at typical temperatures (500-700°C). We present optical and electrical properties of about 200 nm thick ZnO grown by Atomic Layer Deposition at low temperature range between 100 and 200°C. We demonstrate that ZnO films deposited in this temperature range reveal controllable electrical properties, which strongly depend on growth temperature. Ellipsometric measurements show that dielectric constants and energy gap of such films scale with growth temperature and the bandgap of films deposited at 100°C is about 100 meV narrower than the bandgap of ZnO films deposited at 200°C. This is correlated with low carrier concentration which is at the level of 1016 cm-3. Acknowledgements. The work was supported by the Polish National Science Centre (NCN) based on the decision No. DEC-2012/07/B/ST3/03567 and by the EU 7th FP REGPOT project INERA (GA3 16309).

Authors : M.M. Solovan 1), O.L. Maslyanchuk 1), P.D. Maryanchuk1), V.V. Kulchynsky 1), V.А. Gnatyuk 2,3), T. Aoki 3)
Affiliations : 1) Chernivtsi National University, 2 Kotsyubinsky Str., Chernivtsi 58012, Ukraine; 2) Institute of Semiconductor Physics of NAS of Ukraine, Prospekt Nauky 41, Kyiv 03028, Ukraine; 3) Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432 8011, Japan

Resume : Semi-insulating cadmium telluride (CdTe) is the most important material for widely used detectors of different types of radiation. It is known, the formation of an ohmic contact to a p-type CdTe crystal faces obstacles because in this case, it is necessary to use a metal with a too high work function. Molybdenum oxide (MoO) has found its wide practical application as an interlayer material for the fabrication of a high quality electrical contact to low resistance p-CdTe. Due to large work function (5.2-6 eV) MoO is a promising candidate for the role of the contact material to semi-insulating p-CdTe. This paper reports on the applications of molybdenum oxide thin films in combination with semiinsulating CdTe. The near-ohmic contacts were prepared by the DC magnetron sputtering of MoO thin films onto p-CdTe wafers produced by Acrorad Co., Ltd. Surface morphology and structural properties of the Mo-MoO/р+/р-CdTe near-ohmic contacts were investigated. The analysis of DC and AC electrical characteristics of the heterostructures was carried out. We have shown that the detectors under study are capable of detecting X-/γ-radiation. This research was supported by the NATO Science for Peace and Security Programme (Project SENERA SfP-984705).

Authors : Takahiro Nagata1, Oliver Bierwagen2, Zbigniew Galazka3, Sigenori Ueda4, Hideki Yoshikawa4, Yoshiyuki Yamashita1, Toyohiro Chikyow1
Affiliations : 1 International Center for Materials Nanoarchitectonics, National Institute for Materials Science (WPI-MANA), Japan; 2 Paul-Drude-Institut für Festkörperelektronik, Germany; 3 Leibniz Institute for Crystal Growth, Germany; 4 Synchrotron X-ray Station at SPring-8, NIMS, Japan.

Resume : Tin dioxide (SnO2) is transparent in the visible spectrum and has good electrical conductivity. Therefore, it has a great potential for use as a transparent semiconducting oxide. In our previous work, we found the existence of a surface electron accumulation layer (SEAL) on air-exposed, single crystalline SnO2 (101) [1] and (110) heteroepitaxial films. This SEAL likely plays an influential role in SnO2–based gas sensors but hampers Schottky-contact based applications. Understanding the origin of the SEAL, e.g. intrinsic or due to defects or adsorbates, would bring these oxides into practical semiconductor device applications. In this work, we investigated electronic states of bulk SnO2 single crystals by hard x-ray photoelectron spectroscopy (HAXPES, hν = 5.95 keV) at 300 and 50 K, which can probe the bulk due to the longer mean free path of photoelectrons. As-grown and annealed SnO2 single crystals grown by physical vapor transport (PVT) method were measured with HAXPES at the undulator beamline BL15XU of SPring-8. The HAXPES results revealed that, in contrast to our epitaxial films, both as-grown and post-annealed samples showed no SEAL layer at the in-air cleaved (001) surface. The details of chemical bonding states and the temperature dependence of HAXPES will be discussed. The HAXPES measurements were performed under the approval of the NIMS Synchrotron X-ray Station (Proposal Nos. 2014A4600, 2015A4601). [1] T. Nagata et. al., Appl. Phys. Lett. 98, 232107 (2011).

Authors : I.S. Virt 1,2, L. Glowa 3, S. Gorny 3, M. Bester 3
Affiliations : 1. Department of Experimental Physics, Center for Innovation and Transfer of Natural Sciences and Engineering Knowledge, University of Rzeszow, Rzeszow, Poland 2. Drogobych State Pedagogical University, Ukraine, 3. Department of Biophysics, Center for Innovation and Transfer of Natural Sciences and Engineering Knowledge, University of Rzeszow, Rzeszow, Poland,

Resume : The aim of this research is to use band gap engineering techniques to investigate the possibilities to reduce the thermal generation and thereby improve the signal-to noise ratio so that operation at room temperature becomes possible. The films with governed doping impurities are of much practical interest for this purpose. Films doping by means of diffusion from the substrate. The method of noise spectroscopy is one of the prospective techniques of impurities investigations in semiconductors. The study of the noise characteristic of ZnO doped with Co, Cr, Mn are presented here. The spectra of noise power were measured by using four-probe method. Noise spectra of ZnO doping different chemical elements, reveal the monotonous decrease: the noise value is given by the law 1/f^gamma (gamma= 0.9) in the frequency range 10^1 – 10^8 Hz. Nevertheless, in the range of middle frequencies the deviation with gamma <1 is observed for 1/f^gamma function. The level and spectral distribution of the noise density are weakly affected by the impurities type and concentration. We have also registered the higher noise level in the ZnO of solid ternary solution based on ZnO (for example, Zn1-xCoxO, x=0.4) in comparison to other film. Complex character of the spectra point out to the different sources of the noise: exceeding-low-frequency, white, generate-ion-recombination and fraktal-like. The increase of contribution caused by the last two sources is especially sufficient at the relatively high frequencies and clearly observed as a dependence Si(f)*f - f. This contribution increases in the ternary compounds. This fact can be cause by the enlargement of the lattice inhomogeneity (formation of Co-riched cluster is possible). The Hooge constant  is an informative parameter, which, in particular, depends on the type of charge scattering in the lattice. The temperature dependence of low-frequency noise can be presented as a sum of acoustic and optical components determined by two Hooge constants: a and o respectively. Shot noise is caused by the randomness in the flux of carriers crossing the active region of a given device and is associated with discreteness of the electric charge. Especially, the inhomogeneities lead to deviation low-frequency noise from the hyperbolic dependence. In the range of middle frequencies the noise power increases (dependence Si(f)*ff). Such a phenomena is observed also in semiconductors with grain boundaries and becomes (as it follows from the experiments) a typical one for films with macrodefects and inhomogeneities.

Authors : S.Q.Li,1) R. Mohamad,1), J.Chen1), M. B. Ullah,2) V. Avrutin,2) Ü. Özgür, 2) H. Morkoç,2) and P. Ruterana1)
Affiliations : 1CIMAP, UMR 6252 CNRS, ENSICAEN, UCBN, CEA, 6 Boulevard du Maréchal Juin, 14050 Caen Cedex, France 2Department of Electrical and Computer Engineering, Virginia Commonwealth University, Richmond, Virginia 23284, USA

Resume : Wurtzite ZnO with a band gap ~3.3eV at room temperature has attracted a great deal of attention for light emitter applications, notwithstanding the lack of stable p-doping. (0001)-GaN/c-sapphire templates have become good candidates for epitaxial ZnO films owing to their high structural quality with a moderate lattice mismatch of 1.9%. Zn-polar ZnO, which is preferred for the fabrication of ZnO-based heterojunction high mobility 2D electron gas transistors, can be achieved on Ga-polar GaN. In this work, we have succeeded in the two-dimensional growth of both O- and Zn-polar ZnO epilayers on Ga-polar GaN/c-sapphire templates by controlling oxygen to Zn flux ratio during ZnO nucleation. A detailed high resolution transmission electron microscopy investigation has been carried out in order to determine the mechanisms that underlie the polarity inversion occurring in O-polar ZnO on Ga-polar GaN. It was revealed that the change takes place within one to three monolayers at the GaN/ZnO interface. For clarifying the atomic bonding of interfacial Ga-N, Ga-O, O-Zn, Electron Energy Loss Spectrum (EELS) and elemental EDS mapping have been used. This experimental investigation is carried out along with an atomistic modelling of the interfacial phenomena using molecular dynamics using modified Stillinger-Weber potentials. We propose a chemical and electronic structure of this interfacial transformation.

Authors : Oliver Bierwagen1, Carsten Tschammer1, Manfred Ramsteiner1, Martin Feneberg2, Rüdiger Goldhahn2
Affiliations : 1 Paul-Drude-Institut für Festkörperelektronik, Berlin, Germany.; 2 Institut für Experimentelle Physik, Otto-von-Guericke-Universität, Magdeburg, Germany.

Resume : NiO is a transparent semiconducting oxide with unintentional p-type conductivity. Currently, NiO is used in batteries, capacitors as well as gas sensors and is considered for future applications in UV-detectors, all-oxide hetero pn-diodes, and organic solar cells. For the latter, NiO is an excellent candidate as an interfacial layer between the ITO anode and the active organic layer, serving as electron blocking and hole transport layer. Here, unintentionally doped NiO thin layers were grown by plasma-assisted molecular beam epitaxy. For the well-defined epitaxy of NiO(100) layers and surfaces, MgO(100) was chosen as substrate due to their common crystal structure with low lattice mismatch. The resulting crystal structure and surface morphology were investigated by X-ray diffraction and atomic force microscopy as well as scanning electron microscopy, respectively. Raman spectroscopy was used to assess the content of symmetry-breaking lattice defects. The optical band gap and layer conductivity were determined by spectroscopic ellipsometry and DC current-voltage measurements, respectively. Near stoichiometric (green) bulk NiO was measured as a reference. The layer properties as a function of growth temperature and oxygen-to-Ni-flux will be discussed and conclusions on unintentional doping and lattice defects will be drawn.

Authors : A.A. Tikhii, Yu.M. Nikolaenko, Yu.I. Zhikhareva, I.V. Zhikharev
Affiliations : Donetsk Institute for Physics and Engineering named after O.O. Galkin, 83114 Donetsk, Ukraine; Donetsk Institute for Physics and Engineering named after O.O. Galkin, 83114 Donetsk, Ukraine; State University of Telecommunications, 03680 Kyiv, Ukraine; Donetsk Institute for Physics and Engineering named after O.O. Galkin, 83114 Donetsk, Ukraine

Resume : The interest to study of the fundamental absorption edge of the annealed and unannealed In2O3 films is related to the discussion about the band structure and nature of observed "indirect" transitions in these materials. – This transitions probably associated with the imperfections of the material structure [1, 2]. The films produced by dc-magnetron sputtering on the substrates of Al2O3 (012). The deposition time was 1 h; current – 50 mA; voltage - 300 V, for all films. The temperature of substrates was varied in the range of 20 – 600 °C for different films. The unannealed films have smaller direct and "indirect" band gap when higher substrate temperature used (4.07 eV and 2.73 eV at 20 °C; 3.7 eV and 2.46 eV at 600 °C, accordingly). These results are quite natural – the films deposited on the "hot" (600 °C) substrates are less defective. Annealing leads films to unification in the band gap. The direct and "indirect" band gap decrease to 3.6 and 2.35, accordingly. This explained by the decrease of influence of the barriers in the annealed films. But the energy difference between the direct and "indirect" transitions weakly depends on the substrate temperature and annealing. The latter is hardly consistent with the conclusions of [2] and demonstrates the need for further research of electronic transitions in the indium oxide. [1] Erhart P., Klean A., Egdell R. G., Albe K., Phys. Rev. B, 75, 153205 (2007). [2] Klein A., Appl. Phys. Lett., 77, 2009 (2000)

Authors : , Kadidja CHEDELA1, Rachid GHERIANI1 Boubekar BENHAOUA2
Affiliations : 1 LRPPS Laboratory, University of Ouargla, Algeria; 2 University of El-Ouad, Algeria

Resume : Among transparent conductive oxide TCO materials, we can include zinc oxide (ZnO) with interesting physical properties, which places it among the most promising materials for use in various fields such as piezoelectricity, photovoltaic effect and optoelectronics. In this work, we have prepared two series, undoped and La doped ZnO thin films, with flowing concentrations by weight = 0, 1, 2, 3 and 5. LaCl3 was used as source of dopant in the precursor of Zn 2which was obtained by dissolving zinc acetate in 1:1 methanol-double distilled water. During deposition by spray pyrolysis technique, glass substrates were kept out at 375 °C. A fundamental study of their structural and opto-electrical properties such as crystallization, optical transmittance spectra, energy gap and grain size of these materials were realized using XRD and Vis. UV. X-ray diffraction analysis showed that all the films are polycrystalline with a hexagonal wurtzite structure with (002) preferred orientation. Spectrophotometric measurements in Vis. UV range have showed that all the films have a high transmission of about 85% in the visible zone with a band gap energy ranged in (3.28 -3.3) eV. It was found that the disorder of defects in the structure surveyed by deducting the Urbuch energy did not affect the energy band gap ranged in ((56.05-86.98 meV. FTIR measurements showed the presence of Zn-O vibration bands at the interval ( 400 -700 cm-1). The results showed that the increase in dopant concentration leads to a slight shift in the peaks positions. Keywords: TCO, zinc oxide ,spray pyrolysis , DRX, UV, FTIR

Authors : P. Prepelita, D. Craciun, F. Garoi, V. Craciun
Affiliations : National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Street, PO Box MG-36, 077125 Magurele, Ilfov, Romania

Resume : Transparent conductive oxides (e.g. ITO thin films), with thickness values in the range 230 – 370 nm, were prepared onto glass substrates using the rf magnetron sputtering technique. After deposition, the samples were RTA in air at temperatures up to 723K. In this study, a stylus profilometer (Ambios, XP–2) was used to measure the thickness of the oxide thin films. The structural (i.e. XRD, GIXRD, SEM and AFM), optical (i.e. transmission spectra ) and electrical (i.e. I-V characteristic) properties of both as-deposited and annealed samples were investigated. The surface morphology of the samples appeared as granular and polycrystalline with high optical transparency and a good electrical conductivity. Influences of post deposition thermal treatment on morphological properties of these oxides were discussed based on XRD measurements. Double-beam configuration transmittance spectra were recorded in the 190 – 3000 nm wavelength range and, consequently, several optical constants (i.e. Drude damping coefficient, Drude frequency, complex permittivity, refractive indices, extinction coefficients) were obtained for samples with various thicknesses. Optical properties of these oxide films in the near infrared (NIR) range were described by the Drude free electron model. A computational algorithm for oxides thin films using computational models (Swanepoel and Wemple DiDomenico model) was developed and optical properties were investigated. Depending on the preparation conditions and the annealing temperature, value of the optical bandgap, Eg, of the corresponding thin films ranged between 3.35 eV and 3.65 eV. The electrical conductivity was measured using the four points method. An electrical analysis of the conduction mechanisms specific for different voltage ranges was also performed. These oxide films present interesting optoelectronic properties in terms of basic research and related applications of plasmonic metamaterials.

Authors : T. Xiao1, H. Scherg-Kurmes1,2, S. Körner1,2, M. Meixner1, X. Kozina1,3, E. Ikenaga3, R. Félix1, X.X. Liao1, R.G. Wilks1,4, B. Szyszka2, and M. Bär1,4,5
Affiliations : 1Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 14109 Berlin, Germany; 2Technologie für Dünnschicht-Bauelemente, Technische Universität Berlin, 10587 Berlin, Germany; 3SPring-8/JASRI 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan; 4Energy Materials In-Situ Laboratory Berlin (EMIL), Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin, Germany; 5Institut für Physik und Chemie, Brandenburgische Technische Universität Cottbus-Senftenberg, 03046 Cottbus, Germany;

Resume : The transparent conductive oxide (TCO) indium oxide (In2O3) has widespread applications in optical displays and photovoltaic devices due to its high optical transparency in the visible region and its high electrical conductivity.1-3 Generally, the conductivity of In2O3 films can be tuned through doping.4, 5 In this work, films of intrinsic (i.e., not intentionally doped) and n-type doped (by Sn or H) In2O3 variants are prepared by RF magnetron sputtering, and their (optoelectronic) structures are investigated before and after annealing using lab-based x-ray diffraction, ellipsometry, synchrotron-based hard x-ray photoelectron spectroscopy (HAXPES), and Hall measurements. The shape of the In 3d5/2 HAXPES line is observed to be asymmetric for all samples before and after annealing, which is interpreted in terms of a screening mechanism that depends on the amount of charge carriers. All valence band (VB) spectra show significant density of states (DOS) above the VB maximum (VBM) close to the Fermi level, which we ascribe to occupied defect and/or conduction band (CB) states. The intensity of these spectral features is higher (and before annealing similar) for the n-type doped compared to the intrinsic In2O3 material. Upon annealing the VB spectrum of the H-doped In2O3 changes most – in particular the above VBM DOS significantly decreases, indicating a change in defect chemistry and/or charge carrier concentration. Accompanying x-ray diffraction measurements indicate the crystalline and amorphous nature of the In2O3 and the Sn-doped In2O3 samples, respectively, independent of annealing. For the H-doped In2O3, we however see an annealing-induced crystallization of the material. At the same time, Hall measurements show that the carrier concentration is reduced by a factor of approx. 2 and the charge carrier mobility increases by a factor of approx. 3 to 127 cm2/Vs. In our contribution, we will discuss the implications for the optoelectronic properties (that are relevant – and thus need to be considered – for degenerative doped semiconductors, such as the Burstein-Moss [BM] shift6 and the band-gap renormalization [BGR] effect7) in order to relate the HAXPES derived VBM positions to the optically derived band gap values. We find that the BM shift is almost offset by the BGR effect due to the similar effective masses in the CB and VB. 1I. Hamberg and C. G. Granqvist, J. Appl. Phys. 60, R123 (1986). 2C. G. Granqvist and A. Hultäker, Thin Solid Films 411, 1 (2002). 3G. Thomas, Nature (London) 389, 907 (1997). 4J. H. W. de Wit, J. Solid State Chem. 13, 192 (1975). 5S. Limpijumnong, P. Reunchan, A. Janotti, and C. G. Van de Wall, Phys. Rev. B 80, 193202 (2009). 6E. Burstein, Phys. Rev. B 93, 632 (1954). 7P. Schmid, Phys. Rev. B 23, 5531 (1981).

Authors : Penka Terziyska, Blagoy Blagoev, Anna Szekeres, Dimiter Dimitrov and Vladimir Mehandzhiev
Affiliations : Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd, 1784 Sofia, Bulgaria

Resume : Abstract Zinc oxide films are of great interest for electronic and optoelectronic device applications. Control of their electrical and optical properties is of great interest from scientific and applied point of view. We present spectroscopic ellipsometry study of zinc oxide films doped with aluminum (AZO), deposited on silicon substrates by Atomic Layer Deposition at 200°C deposition temperature. The thickness of the AZO layers is about 200 nm. The volume concentration of Al2O3 for the investigated layers varies from 0 to 3.39%. The calculated optical bang gap is around 3.31eV and increases with the Al content. The wavelength dispersion curves of the refractive index and the extinction coefficient of the ZnO layers as well as the dielectric functions will be presented. A shift of the ε1 peak toward the higher energies with increasing the Al content is observed due to the Moss-Burstein effect. Thickness maps of the ZnO films deposited on 4 inch Si wafer showing good thickness homogeneity will also be presented. Acknowledgements: This work was supported by the EU 7th FP INERA REGPOT-2012-2013-1 NMP Research and Innovation Capacity Strengthening of ISSP-BAS in Multifunctional Nanostructures

Authors : A.N. Papathanassiou (1), I. Sakellis (1), E.Vitoratos (2), S. Sakkopoulos (2)
Affiliations : (1) National and Kapodistrian University of Athens, Physics Department, Solid State Physics Section Greece; (2) University of Patras, Physics Department, 28500 Patras, Greece

Resume : The effect of composition on interfacial polarization phenomena in polypyrrole/zinc oxide composites was investigated by complex permittivity measurements in the frequency range 10 mHz to 1 MHz Cooling from room temperature to 15 K results in the suppression of the dc conductivity and the identification of dielectric relaxation mechanisms. For 20, 30 and 40 wt % ZnO composites, a high frequency relaxation was detected in the range 10 - 100 k Hz.. Its characteristic mean relaxation time and its concentration dependence are compatible with theoretical redictions for interfacial polarization. For the last two composites mentioned above, an additional low-frequency relaxation appears about the frequency range 10 mHz - 10 Hz and is ascribed to space charge relaxation. The temperature evolution of the relaxation mechanisms studied at different isothermal conditions provides information about the dynamics of relaxing charge carriers. Composites loaded with 10 wt % ZnO are most proper optoelectronic material for electric charge percolation, since they combine good electrical conduction, poor capacitance effects and ohmic sample-electrode contacts.

Authors : S. Prucnal1, M. Wang1, F. Liu1, Jiada Wu2, Hua Cai2, S. Zhou1 and W. Skorupa1
Affiliations : 1Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, Germany 2 Department of Optical Science and Engineering, Fudan University, Shanghai 200433, People’s Republic of China

Resume : To these days ZnO is one of the most widely investigated types of transparent conductive oxides except ITO. The electronic structure of most of the native defects in ZnO was studied both theoretically and experimentally using various methods. Based on simulation and experimental results, A. Sokol, et al., , have proposed a complex model for the electronic structure of different point defects in doped and undoped ZnO [Faraday Discuss., 134, 267-282 (2007)]. There is agreement that the zinc interstitial (Zni) is a shallow donor and is mainly responsible for the n-type conductivity of intrinsic ZnO. The oxygen interstitial (Oi) is neutral in ZnO, has the energy level located about 2.8 eV below the bottom of the conduction band, and is mainly responsible for the blue-green emission at 2.5 – 2.3 eV. But the energy levels of exited Zni* and Oi are controversial. Using density functional theory calculations, Yong-Sung Kim and C. H. Park have shown that Zni* should have an energy level above the conduction band but to this day it has not been proven experimentally and the exact energy position is unknown [Phys. Rev. Lett. 102, 086403 (2009)]. In order to verify their theory we have performed detailed optical and electrical investigations of ZnO films deposited on insulating Si wafers by reactive pulsed laser deposition. The defect engineering in ZnO was performed using non-equilibrium flash lamp annealing operated in the millisecond range with different annealing ambient. Temperature dependent photoluminescence (PL) emission and excitation (PLE) were utilised to determine the radiative transitions and excitation levels in ZnO, respectively. In order to determine the carrier concentration and conductivity type of processed ZnO films, Hall Effect measurements were performed in the temperature range from 3 to 300K. According to PLE the first excited levels of Zni* and Oi are located at 0.83 eV and 0.70 eV above the conduction band, respectively. The concentration of Zni* and Oi is determined by the annealing atmosphere. The oxygen-poor atmosphere promotes the Zn-interstitial formation while annealing in oxygen suppresses the n-type defects and increases the Oi concentration. Comparison of temperature dependent PL and Hall Effect data confirms that the Zni is a main intrinsic source of n-type conduction in ZnO.

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Authors : Hideo Hosono
Affiliations : Tokyo Institute of Technology

Resume : Creating novel functionality utilizing abundant element is a major challenge in material research. 12CaO∙7Al2O3(C12A7) with a crystal structure composed of 3D-connected sub-nanometer-sized cages entrapping oxygen ions as the counter anion is an insulator with a band gap of ~7eV. We have attempted to realize novel functionalities by replacing these oxygen ions with unconventional anions such as O-, H- and electron. C12A7:O- and C12A7:H- exhibit high oxidation power enough to oxidize Pt and light-induced insulator-electronic conductor conversion, respectively. The striking results were obtained for C12A7:e-, a first RT electride ; the conductivity at RT is changed from ~E-10 to E+3 Scm-1 and metal-superconductor transition occurs at low temperatures. The most unique property is its low work function of 2.4eV, comparable to metal potassium, but chemically stable. This property led to the finding of high performance catalyst for ammonia synthesis at ambient pressure when Ru nanoparticles are loaded on the surface of C12A7:e-. A series of finding on electro-active functionality in C12A7 demonstrated the power of nanostructure composed of abundant elements and may be regarded as a pioneering research of “Element Strategy Initiative”, a Japan-original science and technology project. We expect the recent discovery of 2D-electride Ca2N and Y2C along with material design concept would open a new frontier. Recently, we have created amorphous C12A7:e thin films by sputtering. The resulting thin films are optically transparent but retain a low work function (~3.0eV). Such a unique properties meet the requirement for electron injection layers of inverted-type OLEDs. In this talk I show the recent advances in science and application of C12A7:e along with the background.

Authors : Christina Scheu
Affiliations : Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany

Resume : Within the last years several concepts were developed for creating environmentally friendly energy sources, such as photovoltaics, fuel cells, and photo-electrochemical cells, which are based on novel nanostructured morphologies and material combinations. For these energy conversion systems semiconducting oxide nanostructures are of great interest since they can be used as e.g. electrode materials or photocatalysts. The occurring interfaces and defects within the nanostructures are the key parameters which determine the functionality and limit charge carrier separation and charge transport. To improve the performance, the inorganic nanostructures can be modified by e.g. doping and/or by creating core-shell structures. Annealing treatments can be performed to minimize defects and to induce phase transformation leading to crystal modifications with a more suitable band gap. Two examples will be presented in this talk, Nb3O7(OH) [1] and TiO2 [2,3] nanowire arrays which can be applied as electrode material in dye sensitized hybrid solar cells and in light induced water-splitting devices. The nanostructures were synthesized hydrothermally. Different advanced transmission electron microscopy (TEM) techniques were applied to study the crystal structure, atomic arrangement, chemical composition, bonding behavior and band gap of the individual nanowires and networks on the atomic scale The results were correlated to the synthesis conditions and used to construct growth models. In addition, the functional properties of the Nb3O7(OH) and TiO2 nanostructures were measured in photo-electrochemical and dye sensitized hybrid solar cells. The properties like charge carrier mobility and lifetime were evaluated and further improved by using modified systems developed with the insights obtained by TEM [3]. [1] S. B. Betzler, A. Wisnet, B. Breitbach, C. Mitterbauer, J. Weickert, L. Schmidt-Mende, and C. Scheu, J. Mater. Chem. A, 2014, 2, 12005 [2] A. Wisnet, S. B. Betzler, R. V. Zucker, J. A. Dorman, P. Wagatha, S. Matich, E.Okunishi, L. Schmidt-Mende, and C. Scheu, Cryst. Growth & Design, 2014, 14(9), 4658. [3] A. Wisnet, K. Bader, S. B. Betzler, M. Handloser, J. Weickert, A. Hartschuh, L. Schmidt-Mende, C. Scheu, J. A. Dorman., Adv. Funct. Mater., 2015, 25, 2601. [4] The author would like to thank the colleagues and co-workers who contributed to this work and the German Research Foundation (DFG) for financial support.

Authors : Chris G. Van de Walle
Affiliations : Materials Department, University of California, Santa Barbara, California, USA

Resume : Perovskite oxides have received significant attention in recent years, in part due to their ability to generate very high density two-dimensional electron gases (2DEGs) at interfaces between polar and nonpolar materials [1]. Most of these complex oxides have degenerate conduction bands composed of transition-metal d states, leading to large effective masses and low mobilities, a detriment for electronic applications. BaSnO3 has emerged as an alternative: it crystallizes in the perovskite structure but its conduction band is nondegenerate and composed of Sn s states, resulting in high mobility, favorable for a transparent conductor. I will show how cutting-edge first-principles calculations shed light on the multiple aspects of this problem: band alignment and confinement of the 2DEG [1,2], mobility [3], and for applications requiring transparency, fundamental limits on absorption [4]. Work performed in collaboration with B. Himmetoglu, A. Janotti, E. Kioupakis, K. Krishnaswamy, and H. Peelaers, and supported by ONR, DOE, LEAST, and NSF. [1] L. Bjaalie, B. Himmetoglu, L. Weston, A. Janotti and C. G. Van de Walle, New J. Phys. 16, 025005 (2014). [2] K. Krishnaswamy, L. Bjaalie, B. Himmetoglu, A. Janotti, L. Gordon, and C. G. Van de Walle, Appl. Phys. Lett. 108, 083501 (2016). [3] B. Himmetoglu, A. Janotti, H. Peelaers, A. Alkauskas, and C. G. Van de Walle, Phys. Rev. B 90, 241204(R) (2014). [4] H. Peelaers, E. Kioupakis, and C.G. Van de Walle, Phys. Rev. B 92, 235201 (2015).

Authors : Simon D. Elliott, Glen Fomengia, Ciaran Murray
Affiliations : Tyndall National Institute, Lee Maltings, Dyke Parade, Cork, T12 R5CP, Ireland

Resume : The stoichiometry of metal cations in complex oxides has a major impact on properties and on their application as functional materials. Synthetic methods must therefore aim at controlling composition. Atomic layer deposition (ALD) is a technique for depositing nanoscale thin films with unparalleled control of thickness, uniformity and conformality. However the control of stoichiometry is not so straightforward. In this talk we show how the cyclic nature of ALD can be exploited to formulate a 'rule of mixtures' for the stoichiometry of ternary oxides in thin film form. We then show how experimental deviations from this rule can be related to chemical reactivity of particular ALD precursors, computed at first principles level (1). This reveals what reactions are taking place at interfaces at the nanoscale. A second major factor affecting oxide properties is morphology, but so far there is little understanding of why certain ALD processes give amorphous films while others give a certain crystal phase. We investigate this question through first principles simulations of the likely surface structures that result from ALD reactions. The system that we study is the deposition of alumina from trimethylaluminium with water or oxygen plasma as co-reagent, where recent data from synchrotron experiments suggest that a nanocrystalline phase is present in the 'amorphous' as-deposited film, which directs the morphology towards the theta-alumina phase on annealing. Our results show that theta-like structural motifs are associated with the incorporation of protons into the film during growth.

Authors : Simon D. Elliott, Glen Fomengia, Ciaran Murray
Affiliations : Tyndall National Institute, Lee Maltings, Dyke Parade, Cork, T12 R5CP, Ireland

Resume : The stoichiometry of metal cations in complex oxides has a major impact on properties and on their application as functional materials. Synthetic methods must therefore aim at controlling composition. Atomic layer deposition (ALD) is a technique for depositing nanoscale thin films with unparalleled control of thickness, uniformity and conformality. However the control of stoichiometry is not so straightforward. In this talk we show how the cyclic nature of ALD can be exploited to formulate a 'rule of mixtures' for the stoichiometry of ternary oxides in thin film form. We then show how experimental deviations from this rule can be related to chemical reactivity of particular ALD precursors, computed at first principles level (1). This reveals what reactions are taking place at interfaces at the nanoscale. A second major factor affecting oxide properties is morphology, but so far there is little understanding of why certain ALD processes give amorphous films while others give a certain crystal phase. We investigate this question through first principles simulations of the likely surface structures that result from ALD reactions. The system that we study is the deposition of alumina from trimethylaluminium with water or oxygen plasma as co-reagent, where recent data from synchrotron experiments suggest that a nanocrystalline phase is present in the 'amorphous' as-deposited film, which directs the morphology towards the theta-alumina phase on annealing. Our results show that theta-like structural motifs are associated with the incorporation of protons into the film during growth.

Authors : Simon D. Elliott, Glen Fomengia, Ciaran Murray
Affiliations : Tyndall National Institute, Lee Maltings, Dyke Parade, Cork, T12 R5CP, Ireland

Resume : The stoichiometry of metal cations in complex oxides has a major impact on properties and on their application as functional materials. Synthetic methods must therefore aim at controlling composition. Atomic layer deposition (ALD) is a technique for depositing nanoscale thin films with unparalleled control of thickness, uniformity and conformality. However the control of stoichiometry is not so straightforward. In this talk we show how the cyclic nature of ALD can be exploited to formulate a 'rule of mixtures' for the stoichiometry of ternary oxides in thin film form. We then show how experimental deviations from this rule can be related to chemical reactivity of particular ALD precursors, computed at first principles level (1). This reveals what reactions are taking place at interfaces at the nanoscale. A second major factor affecting oxide properties is morphology, but so far there is little understanding of why certain ALD processes give amorphous films while others give a certain crystal phase. We investigate this question through first principles simulations of the likely surface structures that result from ALD reactions. The system that we study is the deposition of alumina from trimethylaluminium with water or oxygen plasma as co-reagent, where recent data from synchrotron experiments suggest that a nanocrystalline phase is present in the 'amorphous' as-deposited film, which directs the morphology towards the theta-alumina phase on annealing. Our results show that theta-like structural motifs are associated with the incorporation of protons into the film during growth.


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Symposium organizers
Duncan ALLSOPPUniversity of Bath, Department of Electronic and Electrical Engineering

BA1 7AY United Kingdom
Holger VON WENCKSTERNUniverstät Leipzig

Linnestrasse 5, 04103 Leipzig, Germany
Oliver BIERWAGENPaul-Drude-Institut für Festkörperelektronik

Hausvogteiplatz 5-7, 10117 Berlin, Germany
Simon RUSHWORTHEpivalence Limited

Jaquet-Droz 1 2002 Neuchâtel Switzerland

+41 32 720 5771