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2021 Fall Meeting

Oxides, ferroelectrics


Wide band gap (WBG) materials: theory, growth, characterization, and applications

WBG materials are the subject of intensive research motivated by attractive electrical properties making them promising for electronic applications. The symposium is designed to exchange recent advances in the field of growth, characterization, material properties, theoretical predictions, device fabrication, and system applications.

Wide bandgap (WBG) materials such as Ga2O3, MgO, ZnO, TiO2, GaN and high-k oxides, like ZrO2 and HfO2, have attracted much attention due to their emerging application as an active layer in thin film transistors, light-emitting diodes in the ultraviolet region and as transparent electrodes. The ability to control the physicochemical properties by adjustment of crystallographic structure, arrangement of atoms inside sample's volume and along the surface, taking into account point defects, is of crucial importance from both fundamental and applied research points of view. Extensive knowledge on electronic and optical properties of single crystals, films, nano-objects (like nanowires, nanorods, quantum dots, heterostructures etc.) including interfaces helps us to construct the informational bridge between the structural and electronic properties of materials.

Two major goals of the proposed symposium are to:

  • become a forum for exchanging knowledge and ideas between physicists and materials scientists, as well as experimentalists and theoreticians;
  • provide an overview and establish the current state-of-the-art in applications of such materials.

The presentations will aim to cover the topics:

  • synthesis and crystal growth of single crystals and low-dimensional materials;
  • band structure and lattice defects in crystal thin films and heterostructures;
  • optical, mechanical and thermal properties;
  • electrical properties: doping technology, and transport properties;
  • properties of interface processes studied in situ: (chemical synthesis reactions, phase transitions, catalytic processes).
  • dynamical properties: charge transfer, chemical reactions, etc.
  • theoretical modelling and prediction of properties using, e.g., ab initio and machine learning.
  • prospective applications of the WBG materials in various industrial sectors.

Prospective applications of the WBG materials in various industrial sectors will be discussed, e.g.:

  • high-performance optoelectronic, ultraviolet and electronic devices.
  • high-k oxides based memories
  • sustainable energy and solid-state lighting.
  • catalysis.
  • applications in biology and medicine.

List of confirmed invited speakers:

  • Alex Shluger - Dept of Physics & Astronomy, University College London;
  • Andrej Kuznetsov - Dept of Physics, University of Oslo, Norway;
  • Cesare Franchini - Faculty of Physics, University of Vienna, Austria;
  • Chennupati Jagadish - Australian National University Canberra;
  • John Buckeridge – Division of Electrical & Electronic Engineering, London South Bank University;
  • Kin M. Yu - Dept of Physics & Materials Science, City University of Hong Kong;
  • Marco Kirm - Faculty of Science and Technology, University of Tartu, Estonia;
  • Mikko Ritala - Dept of Chemistry, University of Helsinki,  Finland;
  • Tim Veal - Dept of Physics, University of Liverpool, UK;

List of scientific committee members:

  • Jaan Aarik, Estonian Academy of Sciences, Estonia
  • Davide Barreca, ICMATE-CNR and INSTM, Italy
  • Richard Catlow, University College, UK
  • Hanna Dabkowska, University of Hamilton, Canada
  • Ulrike Diebold, Technishe Uinversity Vienna, Austria
  • Karol Frohlich, Slovak Academy of Sciences, Slovakia
  • Samuel Graham, Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, USA
  • Johannes Heitmann, Technical University Freiberg, Germany
  • Sanjay Mathur, Institute of Inorganic Chemistry, Germany
  • Giafranco Pacchioni, Universita' degli Studi di Milano-Bicocca, Italy
  • Wojciech Paszkowicz, Polish Academy of Sciences, Poland
  • Magdalena Skompska, Warsaw University, Poland
  • Imre Miklos Szilagyi, Budapest University of Technology and Economics, Hungary


Selected papers will be published in a special issue of the journal 'Materials Science in Semiconductor Processing' (Elsevier Ltd.). Impact Factor: 3.085. Accepted papers will appear online immediately (with doi and page numbers) and subsequently be compiled in an online special issue. Submission open from September 15 until October 17, 2021. Attendance to the meeting is mandatory for the papers to be published.

The submission website for 'Materials Science in Semiconductor Processing' (Elsevier Ltd.) can be accessed via the link:

To ensure that all manuscripts are correctly identified for inclusion into the special issue, it is important that authors select the following specific article type: 

VSI: WBG materials - Research Paper
Selection of this will be the first step of your submission process, followed by standard steps of providing details, uploading and submitting of your manuscripts.

Submission is open already and will stay open until November 14, 2021.

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08:20 Welcome message and introduction to the Symposium    
II-VI Based Materials I : Chairs: Tadeusz Suski, Iraida N. Demchenko
Authors : Yu, K. M.
Affiliations : Department of Physics, City University of Hong Kong

Resume : Oxide-based transparent p−n homojunctions are desirable for the development of transparent electronics. However, most oxide semiconductors are intrinsically n-type and obtaining a reliable p-type wide-gap oxide is still challenging. This can be attributed to the low energy location and the rather flat dispersion of the O 2p orbitals derived valence band (VB) of most transition metal (TM) oxides. Consequently, the development of transparent oxide-based optoelectronic devices is largely hampered by the lack of wide-gap oxides which can achieve both p- and n- (bipolar) conductivity. Here, we showed that by alloying oxides with different electronic band structures, it is possible to achieve bipolar doping in wide gap ternary oxides. Among wide gap oxides, cadmium oxide (CdO) can be doped heavily n-type and has the highest reported electron mobility while nickel oxide (NiO) is one of the very few known p-type TM oxides. Furthermore, NiO has the same rocksalt (RS) structure as CdO, but its valence band maximum (VBM) is ~1 eV above the conduction band minimum (VBM) of CdO. Hence, alloys of these two oxides with a type III band offset can offer a unique opportunity for the development of wide gap ternary oxides which can exhibit both n- and p- conductivity. We found that the conduction type of NixCd1-xO alloy thin films depends on the alloy composition and oxygen stoichiometry. We demonstrated that in the composition range of 0.381 eV above that of the WZ phase, so that alloys with similar composition with the two different structures exhibit a type II band offset. The much higher VBM position of RS alloys favors the formation of native acceptor defects as well as efficient extrinsic p-type doping. Our results offer interesting opportunities for using these alloys for transparent devices that require bipolar conductivity.

Authors : S. Mishra*, A. Adhikari, E. Przezdziecka, W. Paszkowicz, A. Sulich, R. Jakiela, M. Ozga and E. Guziewicz
Affiliations : Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland

Resume : Versatile ZnO semiconducting films with well-defined structural qualities, tunable electrical and optical properties are needed for device applications. However, unintentional structural and point defects and impurities present in ZnO films are main obstructions in achieving controllability, repeatability, and carrier transport in this material [1]. The aim of the present study was to find out relationship between structure and conductivity of thin polycrystalline ZnO films grown under O- or Zn-rich conditions. Two series of ~100 nm thick ZnO films were grown by Atomic Layer Deposition on Si and a-Al2O3 substrates at growth temperature (Tg) range of ~100-300oC. RT-Hall measurements revealed that resistivity increased with Tg and also after rapid thermal annealing (RTP) for both ZnO/Si as well as ZnO/a-Al2O3 films. SIMS experiments found that the content of unintentional H impurity in both as grown and annealed films is higher than the carrier concentrations, showing that not all H atoms play a role of a donor. There exist a certain Tg range of ~160-200oC where preferred orientation showed switching phenomenon influencing conductivity of the films. Strain, dislocation density, and Urbach energy [2] calculations showed that films formed at Tg~160oC had better crystalline quality and higher electrical conductivity, as well as the carrier mobility for both series. Overall, when compared to ZnO/a-Al2O3, the ZnO/Si films showed lower strain and lower dislocation density. Acknowledgement. The work has been performed within the National Science Centre project No. 2018/31/B/ST3/03576. [1] E. Przezdziecka, E. Guziewicz, D. Jarosz, D. Snigurenko, Sulich, P. Sybilski, R. Jakiela and W. Paszkowicz, J. Appl. Phys. 127, 075104 (2020) [2] A. Adhikari, E. Przezdziecka, S. Mishra, P. Sybilski, J.M. Sajkowski and E. Guziewicz, Phys. Stat. Sol. A, 2000669, (2021)

Authors : R. Magrin Maffei (1,2), S. Benedetti (2), A. Di Bona (2), M. Sygletou (3), F. Bisio (4), S. D’Addato (2)
Affiliations : (1) CNR, Istituto Nanoscienze, Via G. Campi 213/a, 41125 Modena, Italy; (2) Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Università di Modena e Reggio Emilia, via Giuseppe Campi 213/a, 41125 Modena, Italy; (3) OptMatLab, Dipartimento di Fisica, Università di Genova, via Dodecaneso 33, 16146 Genova, Italy; (4) CNR-SPIN, Perrone 24, 16152 Genova, Italy

Resume : Among wide-band gap semiconductors, Transparent Conducting Oxides (TCO) are of utmost interest thanks to their optical transparency and low electrical resistivity, that makes them uniquely appealing for applications in optoelectronics, photovoltaics and energy harvesting [1, 2]. One of their peculiarities is the wide tunability of their electrical and optical properties through doping. Typically, TCO films are polycrystalline. However, the growth of epitaxial films would improve conductivity and carrier mobility, especially in thin films, since a good crystalline order is expected to reduce grain boundary scattering as well as trapping of carriers at grain boundaries. Thick epitaxial Al-doped ZnO (AZO) films have been grown via various techniques, exploiting an epitaxial substrate [3, 4]. In our study, we grew AZO films of thickness from 300 nm down to 30 nm on Strontium Titanate (SrTiO3) substrates via Radio Frequency (RF) Magnetron sputtering with optimized conditions to obtain epitaxy and improve carrier density and mobility. The growth was carried out at 400 C. As a reference, we grew polycrystalline AZO films with the same conditions on silicon dioxide (SiO2) amorphous substrates. We investigated surface roughness and mean size of grains of the films with Atomic Force Microscopy (AFM), crystalline order and quality with High Resolution X-Ray Diffraction (HRXRD) and electrical properties by 4W Probe and Hall measurements. Films grow with a clear epitaxial relationship with the substrate, and this happens even for the thinner samples. As a consequence of the improved crystal order the epitaxial films show a resistivity decreased by two orders of magnitude and increased carrier mobility as compared to polycrystalline films on SiO2. The experimental study of the AZO films was completed with optical characterization through ellipsometry measurements. [1] R. A. Afre et al., Rev. Adv. Mater. Sci. 53 (2018) [2] Y. Chen, IOP Conf. Ser.: Mater. Sci. Eng. 423, 012170 (2018) [3] L. M. Trinca et al., Appl. Surf. Sci. 364 (2016) [4] I. Valenti et al., J. Appl. Phys. 118, 165304 (2015)

Authors : G. El Hallani1, M. Khuili 2, S. Nasih3, N. Fazouan1,3*, A. Liba1, L. Laanab 4, O. Mounkachi 5, A. Mzerd 6, E. H. Atmani 3
Affiliations : 1-Physical Materials Laboratory. Faculty of Sciences and Technologies, Beni Mellal, Morocco 2-Superior School of Technology (EST-Khenifra) khénifra, Morocco 3-Physics of Condensed Matters and Renewables Energies Laboratory. Faculty of Sciences and Technologies, Mohammedia, Morocco 4-Conception Systems Laboratory, Faculty of Sciences, Rabat, Morocco 5-Condensed Matter and Interdisciplinary Sciences Laboratory, Faculty of Sciences, Rabat, Morocco 6- Group of Semiconductors and Environmental Sensor Technologies-Energy Research Center, Faculty of Science, Rabat, Morocco

Resume : Transparent Conductive Oxides (TCO) in solar cells are used as transparent electrodes. They must necessarily have a high optical transmission in order to allow efficient transport of photons to the active layer and also good electrical conductivity which is required to obtain the least losses of transport of photo-generated charges. Aluminum, Magnesium and Tin doped ZnO thin films are some of these. In this contribution, the TCO materials formed of Al, Mg and Sn doped ZnO thin films (AZO, MZO, TZO) were synthesized by spin coating method. The structural, optical and electrical properties of these films are investigated as a function of dopant concentration. X-ray diffraction patterns show that all AZO, MZO and TZO films exhibit the hexagonal würtzite structure with a preferential orientation along [002] direction with no additional peak corresponding to secondary phases. The surface morphologies show that AZO and MZO films are homogeneous and dense while TZO films showed different surface morphologies going from homogeneous to porous structure depending on Sn concentration. An enhancement of optical transmittance of about 95% with a blue shift of the gap energy was found for both Al and Mg doped ZnO layers against 70% of average level transmittance and a red shift of optical window for Sn doped ZnO films. Photoluminescence (PL) measurements at room temperature shows excitonic peaks corresponding to the AZO, MZO and TZO films with a low defects level for 1% Al doped ZnO compared to MZO and TZO films that showing a large intensive band defects centred around 514 nm characterizing the substitution defects of the zinc atoms by oxygen atoms. Electrical measurements show that all the films present an Ohmic comportment with a best electrical conductivity of 2.45 obtained for 1% AZO in accordance with the photoluminescence analysis. The reduced electrical conductivity shown in our films is attributed to the low mobility of charge carriers due to their diffusion by the grain boundaries.

Authors : Quang Chieu BUI (1, 2, 3), Gustavo ARDILA (2), Eirini SARIGIANNIDOU (1), Hervé ROUSSEL (1), Carmen JIMÉNEZ (1), Odette CHAIX-PLUCHERY (1), Xavier MESCOT (2), Fabrice DONATINI (4), Bassem SALEM (3), and Vincent CONSONNI (1).
Affiliations : 1. Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, F-38000 Grenoble, France; 2. Univ. Grenoble Alpes, CNRS, Grenoble INP, IMEP-LAHC, F-38000 Grenoble, France; 3. Univ. Grenoble Alpes, CNRS, LTM, F-38054 Grenoble, France; 4. Univ. Grenoble Alpes, CNRS, Institut NEEL, F-38000 Grenoble, France;

Resume : Zinc oxide (ZnO) has recently attracted much attention as a sustainable and high potential material for piezoelectric application. It is an abundant and biocompatible semiconducting compound with polar and piezoelectric properties thanks to its wurtzite structure. The piezoelectric properties of ZnO are strongly influenced by its morphology (i.e. shape, dimensions, polarity), but its correlation with the growth processes have not completely been elucidated yet. In this work, we study the morphology transitions of ZnO grown on Si substrate by pulsed-liquid injection metal–organic chemical vapour deposition (PLI-MOCVD) together with the evolution of its structural and piezoelectric properties as a function of the growth temperature as well as the O2 gas and diethylzinc solution flow rates. By only raising the growth temperature, the morphology of ZnO is changed from thin films to nanowires, which is associated with the increase in the piezoelectric amplitude and the improvement of the polarity uniformity as measured by piezo-response force microscopy [1]. Furthermore, the flow rate variation leads to different thin film morphologies with a large change of polarity distribution. These results demonstrate the high ability of the PLI-MOCVD system to tune the ZnO properties as a strong interest for piezoelectric applications. [1] Q. C. Bui et al., ACS Appl. Mater. Interfaces 2020, 12 (26), 29583−29593.

10:00 Live Questions & Answers session 1    
10:30 Break    
Advanced Measurement Techniques and Characterization : Chairs: Alexander Shluger
Authors : Kirm, M.*(1)
Affiliations : (1) Institute of Physics, University of Tartu, W. Ostwald Str 1, 50411 Tartu, Estonia * lead presenter

Resume : Wide band gap materials play an important role in many different applications from scintillation to high-performance optoelectronic, ultraviolet, electronic devices and solid-state lighting. In order to develop new materials and improve existing ones advanced spectroscopic methods have to be applied for the characterization using tunable excitation by photons in wide energy range. In recent years’ availability of such short-wavelength synchrotron radiation sources as storage rings and free electron lasers grows and user community consisting of researchers from various disciplines incl. materials science, physics and chemistry [1]. In order to perform such advanced research, several endstations for time-resolved luminescence spectroscopy and measurement techniques (a time correlated multiphoton counting) have been developed by us at the MAX IV Laboratory located in Lund, Sweden. One of these setups is permanently mounted at Finnish-Estonian beamline FinEstBeAMS [2], which provides photons in the energy range of 4.5 – 1000 eV enabling to study valence excitation and inner shell excitation of wide gap materials. In a single bunch operation mode the time resolution as short as 160 ps was achieved [3]. A mobile photoluminescence setup has been implemented to the FemtoMAX beamline, where 100 fs 10 keV X-ray photon pulses are available for investigation of ultrafast processes in scintillators close to real operation conditions and the exceptional time resolution of 28 ps can be exploited [4]. The relaxation processes of electronic excitations in novel wide gap hexafluorogermanate scintillators leading to the ultrafast cross- and intraband luminescence with sub-nanosecond lifetime will be discussed in the basis on the results obtained at these setups by time-resolved luminescence methods [3]. The high quality experimental results are analyzed taking into account electronic band structure calculations from publicly available materials property databases (AFLOW, etc.) Also some examples of other advanced wide gap materials for scintillation and optical applications will be presented and discussed. [1] Y. Hwu and G. Margoritondo, J. Synchr. Radiation 28 (2021) 1014-1029. [2] V. Pankratov, R. Pärna, M. Kirm, et al., Radiation Measurements 121 (2019) 91–98. [3] J. Saaring, A. Vanetsev, K. Chernenko, et al., J. Alloys and Compounds (2021) in press. [4] R.M. Turtos, S. Gundacker, S. Omelkov, et al., npj 2D Materials and Applications 3 (2019) 37.

Authors : Fabian Sievers; Stefan Tappertzhofen
Affiliations : Chair for Micro- and Nanoelectronic, Faculty of Electrical Engineering and Information Technology, TU Dortmund University, Germany

Resume : Highly accurate material characterization is crucial for development of novel multi-functional materials such as AlScN or HfO2. Here we report on the three-dimensional characterization of the pyroelectric response of selected wide bandgap materials. Our measurement setup consists of high-bandwidth near- (852 nm and 1064 nm) to far- (9.15 µm) infra-red quantum cascade and Fabry-Perot laser sources. By means of the laser intensity modulation method, we reconstructed the in-depth distribution of the spontaneous polarization with sub-micron resolution. In case of AlScN, our findings indicate that the thermal diffusivity and its temperature-dependence differs significantly from what is reported for pure Aluminum Nitride, which we attribute to the dominant role of the Sc dopants.

Authors : Aline Jolivet (1), Christophe Labbé (1), Cédric Frilay (1), Olivier Debieu (1, 2), Philippe Marie (1), Bryan Horcholle (1), Franck Lemarié (1), Xavier Portier (1), Clara Grygiel (1), Wojciech Jadwisienczak (3), David Ingram (4), Mudit Upadhyay (5), Adrian David (5), Arnaud Fouchet (5), Ulrike Lüders (5), Julien Cardin (1)
Affiliations : (1): CIMAP Normandie Université, ENSICAEN, UNICAEN, CEA, CNRS, 6 Boulevard Maréchal Juin, 14050 Caen Cedex 4, France; (2): Cirimat, 4 allée Emile Monso, BP-44362, 31030 Toulouse Cedex 4, France; (3) School of Electrical Engineering and Computer Science, Ohio University, Athens, Ohio 45701, USA; (4): Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, USA; (5): NORMANDIE UNIV, ENSICAEN, UNICAEN, CNRS, CRISMAT, 14000 CAEN, France

Resume : TiO2 thin films were produced by atomic layer deposition (ALD) since the beginning of the nineties, with a much interest starting from 2004 (1). Indeed, anatase TiO2 thin films having long exciton lifetime, semiconductor nature and a wide indirect band gap of 3.2 eV (1) are attractive for many contemporary applications including Li ion batteries, photocatalysis, dielectric layers in capacitors and transparent conductive oxides (TCO)(1–3). We will report on optical and electrical properties of the anatase TiO2 thin films deposited by ALD on single crystalline silicon substrates for microelectronics applications and on transparent glass substrates for TiO2-based TCO layers having high transparency in the visible range. TiO2 thin films were grown by ALD on (100) oriented n-type silicon and Schott glass substrates in a low deposition temperature (TD) range from 100°C to 300°C with titanium tri-isopropoxide (TTIP) precursor and water as oxidizing agent. As-deposited TiO2 films crystallized in stoichiometric anatase phase on both silicon and glass at TD ≥ 250°C. Performed characterizations (TEM, XRD, RBS, AFM) shown that crystallization is promoted with the increase of TD and the film thickness. Moreover crystallization seems to follow a well-known growth mechanism (4): (i) deposited TiO2 is first amorphous, then after reaching a certain critical thickness, (ii) crystalline nuclei form randomly at the surface. (iii) Then the nuclei seem to grow isotropically through the surrounding and the newly deposited matter. Optical properties such as refractive index, absorption coefficient and band gap energy were analyzed by ellipsometric measurement on silicon and by photospectroscopy transmission measurement on glass using a Tauc-Lorentz dispersion model. Results from both methods are coherent, and show a decrease of the indirect band gap energy with the increase of TD confirming the phase transition from amorphous to the anatase phase2. Regarding the dielectric properties, the relative permittivity ε’ and the loss angle tan δ of TiO2 films were studied as a function of the frequency. ε’ increases with TD, due to the higher crystalline quality of the films. Low losses and low relaxation are observed, indicating a low density of charged defects in the films and a good quality of the dielectric properties. All observed structural, optical and electrical properties of TiO2 thin films are consistent, showing the possibility to get high quality stoichiometric crystallized anatase TiO2 with a low thermal budget by ALD on different substrates. This work paves the way for the integration at low temperatures of this versatile oxide for future devices. 1. Niemelä J-P, Marin G, Karppinen M. Titanium dioxide thin films by atomic layer deposition: a review. Semicond Sci Technol. 2017. 2. Elbahri MB, Kahouli A, Mercey B, Prellier W, Lüders U. Effects of oxygen pressure during deposition on the dielectric properties of amorphous titanium dioxide thin films. J Phys Appl Phys. 2019. 3. Mo S-D, Ching WY. Electronic and optical properties of three phases of titanium dioxide: Rutile, anatase, and brookite. Phys Rev B. 1995. 4. Puurunen RL, Sajavaara T, Santala E, Miikkulainen V, Saukkonen T, Laitinen M, et al. Controlling the Crystallinity and Roughness of Atomic Layer Deposited Titanium Dioxide Films. J Nanosci Nanotechnol. 2011.

Authors : Bojin Lin (1), Yuto Imae(1), Kotaro Hayashi(1), Hnin Lai Lai Aye(1), Hideto Miyake(2), and Yoshihiro Ishitani(1)
Affiliations : (1) Graduate School of Electrical and Electronic Engineering, Chiba University, Japan (2) Graduate School of Regional Innovation Studies, Mie University, Japan

Resume : Selective absorption and thermal radiation resonating with longitudinal optical (LO) phonon from Au-GaAs mesa-type line and space structures was obtained by our group. This result suggests the application of surface microstructures to THz-mid infrared (IR) optical devices of communication and energy conversion. Previously, radiation resonating with surface or interface phonon polariton (IPhP) or frequencies determined by structural properties has been reported; radiation frequency depends on structural properties or emission direction. In comparison, the LO phonon resonant radiation shows no dependence on these factors, which is an advantage in device application. Here, we have an issue that the dependence on material species, in particular III-nitride has stronger interaction of LO phonon with electric field, meaning the possibility of the emergence of IPhP in the metal-semiconductor structures. Further, we have observed the effects of the modulation of dielectric function on the IPhP mode in a previous report. In this report, we discuss the thermal mid-IR radiation from mesa-type metal-GaN stripe structures from the viewpoints of LO phonon and IPhP resonance. Sample A has mesa structures of GaN on sapphire substrate, where the height was 0.5-1.0 m, and stripe widths of GaN and metal of 2.3-3.8m and 6.2-7.7 m, respectively. Mesa structure was fabricated by RIE. Metal was deposited on the bottom and slope regions of the mesa structure. Another type sample B has no metal deposition at the mesa slope region or no mesa etching. IR reflectance and radiation measurements were conducted using a FTIR spectrometer. Radiation observation was conducted at 580 K. Obtained spectrum was calibrated using emission spectra of a graphite plate. The emission spectrum of sample A showed an eminent peak at approximately 690 cm-1, which is not resonating with the LO phonon at approximately 725 cm-1 at 580 K. When emission polar angle was varied from 0 to 45 degree, the peak wavenumber was nearly constant for the s polarization, while two additional emission peaks at higher and lower energy regions were observed for the p polarization. When metal was not deposited on the slope region, no split for the peak at 690 cm-1 and the LO resonating peak was observed in a region of 725 - 730 cm-1. These results indicate IPhP resonance is dominant in the mesa region, while the LO phonon resonating radiation is mainly yielded by the polarization charges at metal-GaN interface in the bottom region of mesa stripes. The observed wavenumbers of IPhP modes are theoretically obtained only when we take into account the modulation of electric permittivity by the formation of interface polarization charges generated by the thermal occupation of the LO phonon. The mode energies of the IPhPs are dominated by the boundary condition of the GaN-metal in the mesa slope region and the lattice vibration resonating with LO phonon. When the emission polar angle is varied, a pair of mesa slopes yield two different angles between the emission direction and the slopes, which matches to the observation of two additional peaks. The permission of these IPhP resonant emissions are not obtained for the metal-GaAs structure because of the small interaction of optical phonon and electric field. FDTD simulation supports our consideration. These results reveal the particular properties of III-nitride system for the function of IR waveguide or emission based on LO phonon and IPhP resonances and using micro metal-semiconductor stripe structures.

Authors : Ilze Aulika, Martins Zubkins, Jelena Butikova, Juris Purans
Affiliations : Institute of Solid State Physis, University of Latvia, Kengaraga 8, LV-1063, Riga, Latvia

Resume : The Tauc’s method [1] is a much-preferred optical band gap (OBG) evaluate method for amorphous (or glassy) materials. However, regardless its clear and simple purpose, it has been routinely and incorrectly applied to study crystalline semiconductors and dielectrics. In Tauc relation the density of electron states is close to the VB and CB extrema and it is proportional to the square root of the photon energy. Assuming a constant dipole transition matrix element, another possibility to determine OBG is to apply the Cody relation [2]. In spite of the method chosen to determine the OBG of either crystalline or amorphous materials, all of them are influenced by the absorption spectrum α(E) and its following data analysis [3]. Recently very nice revision on OBG was published by A. R. Zanatta proposing a unified methodology to its determination for semiconductors by applying the sigmoid-Boltzmann function to fit α(E) and obtain OBG [3], which works well in case the α(E) is measured at high enough photon energies. In this work we propose an alternative by using the Johs-Herzinger generalized critical point model [4] or Herzinger-Jobs parameterized semiconductor (HJPS) oscillator function [5] to directly fit the α(E) spectra. The results are discussed for amorphous and crystalline ZnO, ZnO2 and YHO thin films by applying Tauc, Cody, sigmoid-Boltzmann function and HJPS. ACKNOWLEDGMENTS This research is supported by the Horizon 2020 Project CAMART² under grant agreement No 739508 and ERAF national project “Smart metal-oxide nanocoating and HIPIMS technologies” No References [1] Tauc, J., Grigorovici, R. & Vancu, A. Optical properties and electronic structure of amorphous germanium. phys. stat. sol. (1966) 15(2), 627–637, [2] Cody, G. D., Brooks, B. G. & Abeles, B. Optical absorption above the optical gap of amorphous silicon hydride. Solar Energy Mater. (1982) 8(1–3), 231–240, [3] A. R. Zanatta, Revisiting the optical bandgap of semiconductors and the proposal of a unified methodology to its determination, Scientific Reports (2019) 9:11225, [4] P. Petrik, Parameterization of the dielectric function of semiconductor nanocrystals, Physica B: Condensed Matter (2014) V453, 2-7, [5] Craig M. Herzinger; Blaine D. Johs., DIELECTRIC FUNCTION PARAMETRIC MODEL, AND METHOD OF USE, Patent Number: 5796983 [6] M. Zubkins et al., Amorphous ultra-wide bandgap ZnOx thin films deposited at cryogenic temperatures, J. Appl. Phys. 128, 215303 (2020),

12:30 Live Questions & Answers session 2    
13:00 Break    
II-VI Based Materials II : Chairs: Elzbieta Guziewicz
Authors : Alexander L. Shluger, Jack Strand
Affiliations : Department of Physics and Astronomy, University College London, UK; Applied Materials, Via Meuccio Ruini 9, Reggio Emilia 42122, Italy

Resume : Charge trapping observed at 300 and 77 K in ferroelectric (FE, annealed Al- or Si-doped) and non-ferroelectric (unannealed and/or undoped) HfO2 films grown by atomic layer deposition revealed the presence of “deep” and “shallow” electron traps with volume concentrations in the 10^19-cm^3 range [1]. These results demonstrate a broad spectrum of electron trapping sites present in undoped HfO2 layers. These include deep states with optical depopulation energies in the 2.0–3.5-eV range, but also traps which are thermally depopulated with activation energies below 0.7 eV and around 0.2 eV. The samples typically contain crystalline regions of non-FE (monoclinic, tetragonal, cubic) and orthorhombic FE phases intermixed with amorphous regions. The trap energy depth and marginal sensitivity of their concentration to crystallization annealing or film doping with Si or Al suggests that these traps are associated with boundaries between crystalline grains and interfaces between crystalline and amorphous regions in HfO2 films. To understand these results, we performed density functional theory (DFT) calculations of electron trapping at surfaces of monoclinic, tetragonal, and orthorhombic phases of HfO2 and at interfaces of these grains with amorphous regions. Some of the trap energies are consistent with those predicted for electron polarons in m-HfO2 (Etr ∼ 0.2 eV) [2] and polaron and bi-polaron photo-depopulation energies in the bulk of amorphous HfO2 (2.0–3.5 eV) [3]. The trap states calculated at the interfaces between the crystalline and amorphous regions are consistent with the observed thermal ionization energies (0.7–1.0 eV below the HfO2 CB). This behaviour suggests the trapping sites are related to morphology and disorder in HfO2 films rather than to the oxygen deficiency and support their intrinsic polaronic nature. Their depth is correlated to the extent of oxygen coordination of Hf sites trapping the extra electrons. We suggest a model that at 77 K electrons are initially trapped in shallow polaron states in monoclinic and orthorhombic HfO2. Some of these electrons escape to an electrode while others hop to grain boundaries and eventually end up in amorphous regions, where they are getting trapped at deeper states. [1] R. A. Izmailov et al., Phys. Rev. Mater. 5, 034415 (2021) [2] D. Muñoz Ramo et al., Phys. Rev. Lett. 99, 155504 (2007) [3] J. Strand et al. Nanotechnology 29, 125703 (2018).

Authors : Schmidt, N.*(1), Trstenjak, U.(1), Rushchanskii, K.(2), Dittmann, R.(1), Karthäuser, S.(1)
Affiliations : (1) Forschungszentrum Jülich GmbH, Peter Grünberg Institut 7 (PGI-7), 52425 Jülich, Germany (2) Forschungszentrum Jülich GmbH, Peter Grünberg Institut 1 (PGI-1), 52425 Jülich, Germany * lead presenter (Mail to

Resume : By use of scanning probe microscopy and spectroscopy (STM and STS), X-ray photoelectron spectroscopy (XPS), and theoretical calculations we investigated the topography and electronic properties of sub-monolayer HfO2 films on highly ordered pyrolytic graphite (HOPG). Crystalline HfO2 nanoislands were grown fully oxidized via pulsed laser deposition at elevated temperatures (> 650°C) by van der Waals epitaxy. STS on homogenously formed and well separated nanoislands revealed a bulk-like size of the apparent bandgap. At the same time, in-gap states close to the Fermi level were found. By use of STM with atomic resolution the first nucleation states of HfO2 nanocrystallites (2.7-4.5 Å in diameter) located next to carbon vacancies in the topmost HOPG layer were identified. In addition, carbon incorporation into HfO2 nanocrystallites was indicated by XPS measurements. Using evolutionary algorithm (USPEX) in combination with Vienna Ab Initio Simulation Package (VASP) a series of possible HfmOn(:C) clusters (with m in range from 3 to 10, and n in range from 3 to 22) with and without incorporation of carbon atoms were simulated. By comparison of the lowest-energy structure and the LDOS of the theoretically deduced nanocrystallites with the experimental results the most relevant nuclei formed during the first growth steps of HfO2 were identified. This finding will be of major significance for the practical growth of the dielectric HfO2 on graphene-based devices.

Authors : Alessandro Lauria, Irene Villa, Mauro Fasoli, Anna Vedda, Markus Niederberger
Affiliations : Laboratory for Multifunctional Materials, Department of Materials, ETH Zürich, Vladimir-Prelog-Weg 5, 8093 Zürich, Switzerland ; Department of Materials Science, University of Milano-Bicocca, Via R. Cozzi 55, 20125 Milano, Italy

Resume : Intense recent research efforts are directed toward the development of novel materials morphologies, such as nanoparticles, able to efficiently convert ionizing radiation into light. Fluorescent or scintillating materials attract great interest in lighting technology, solar applications, theranostics and self-lighting photodynamic therapy. Moreover, additive manufacturing advancements suggest the possibility to fabricate nanoparticle-based materials applicable in several fields. Therefore, novel luminescent nanomaterials free from toxic or expensive elements, such as rare earths, are desirable building blocks for promoting future developments in all these fields. In this work, the structural and morphological properties of pure and Ti-doped HfO2 nanoparticles are studied in dependence of calcination temperatures leading to a fine tuning of either morphology and functional defect configuration. Indeed, tuneable optical features are observed in undoped monoclinic HfO2 nanocrystals and their dependence on the structural properties of the material at the nanoscale are disclosed. TEM, XRD, XPS, and surface area data combined with the analysis of the luminescence allowed us to identify the dual nature of the broad emission at 2.5 eV, where an ultrafast defect-related intrinsic luminescence overlaps with a slower emission ascribed to extrinsic Ti impurities.[1] When titanium is employed as luminescence activator, a bright emission is observed under excitation with both UVC radiation and X-rays. [2] These results represent useful insights toward the design of novel promising nanomaterials suitable for rare-earth-free UV pumped white LEDs based on intrinsic defect engineering, and for X-ray triggered oncological therapies by using the Ti (IV)-related bright radioluminescence to excite photosensitizer molecules for singlet oxygen generation. [1] Villa, I.; Vedda, A.; Fasoli, M.; Lorenzi, R.; Kränzlin, N.; Rechberger, F.; Ilari, G.; Primc, D.; Hattendorf, B.; Heiligtag, F. J.; Niederberger, M.; Lauria, A., Size-Dependent Luminescence in HfO2 Nanocrystals: Toward White Emission from Intrinsic Surface Defects. Chem. Mater. 2016, 28 (10), 3245-3253. [2] Villa, I.; Moretti, F.; Fasoli, M.; Rossi, A.; Hattendorf, B.; Dujardin, C.; Niederberger, M.; Vedda, A.; Lauria, A., The Bright X-Ray Stimulated Luminescence of HfO2 Nanocrystals Activated by Ti Ions. Advanced Optical Materials 2020, 8 (1), 1901348.

Authors : F. Caruso (1,2), P. La Torraca (3), L. Larcher(4), G. Tallarida (1), A. Padovani(4), and S. Spiga(1)
Affiliations : (1) Consiglio Nazionale delle Ricerche - Istituto per la Microelettronica e Microsistemi (CNR-IMM), Unit of Agrate Brianza, 20864 Agrate Brianza (MB), Italy. (2) Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, 20125 Milano, Italy. (3) Department of Sciences and Methods for Engineering, University of Modena and Reggio Emilia, 42122 Reggio Emilia, Italy. (4) Applied Materials-MDLx Italy R&D, 42122 Reggio Emilia, Italy.

Resume : Atomic layer deposited (ALD) hafnium oxide (HfO2) based materials are extensively used as insulating or active layers in a multitude of electronic devices. The addition of aluminum to the binary HfO2 has proved to enhance its electrical properties increasing the dielectric permittivity, reducing the leakage current, and improving the reliability. It is known that the electrical properties are strongly correlated to atomic defects, which generate localized electronic states inside the bandgap that act as charge traps. Nevertheless, the effect of the presence of aluminum on the trap properties is still under debate. Different ALD precursors can also strongly affect the material electrical behavior. Here we present the traps characterization of HfO2 and Al-doped HfO2 (AlHfO) -based TaN/oxide/TaN capacitors with four different Al concentrations (from 0% to 20%) and deposited using various precursor combinations. The films are grown in a Savannah reactor (Cambridge Nanotech) at 300°C using trimethylaluminum and (MeCp)2Hf(Me)(OMe) as metal precursors for aluminum and hafnium, respectively, and using either water or ozone as oxygen precursor. The AlHfO films are grown by alternating HfO2 and Al2O3 ALD cycles with different ratios to control the Al content. Defect properties are extracted from current-voltage characteristics using the Ginestra(TM) simulation software, which self-consistently solves the Poisson’s and charge continuity equations considering all the different conduction mechanisms relevant in dielectrics (i.e. direct and Fowler-Nordheim tunneling, conduction/valence band carrier drift, and multi-phonon trap-assisted-tunneling).[1] In every film two kinds of electron traps are detected. In ozone-based films, 2·10^19 traps/cm3 are normally distributed in energy around 1.9eV below the oxide conduction band minimum (CBM), and 1.4·10^19 traps/cm3 are uniformly distributed from 2.4eV to 4eV below the CBM. The presence of aluminum does not affect the traps properties but increases the oxide band gap (from 5.5eV to 6.2eV) and reduces the electron affinity accordingly, leading to the increase of the injection barrier height. The use of water as oxygen source during the oxide deposition introduces 1.4·10^19 cm-3 fixed positive charges uniformly distributed along the dielectric thickness and reduces traps ionization energies by approximately 0.2eV. On the other hand, the different aluminum content, or the use of different oxygen sources, do not impact significantly on the density of the electron traps. [1] P. La Torraca, F. Caruso, A. Padovani, S. Spiga, G. Tallarida, L. Larcher, “Extraction of Defects Properties in Dielectric Materials From I-V Curve Hysteresis”, IEEE Electron Device Lett. 42 (2021) 220-223.

15:15 Live Questions & Answers session 3    
16:00 Break    
Poster Session 1 : Chairs: Yevgen Melikhov
Authors : S. Mishra1*, R. Schifano1, M. Sarwar1, W. Paszkowicz1, A. Sulich1, R. Jakiela1, M. Ożga1, P. Sybilski1 and E. Guziewicz1.
Affiliations : Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland

Resume : Quantum efficiency of direct wide band gap semiconducting optoelectronic devices is determined by the electron and hole recombination time. However, polarization induced electric field inside piezoelectric materials (for example, along the ZnO c-axis) separates the carriers, thus reducing the optical performances [1]. To study in detail the polarity effects on the electrical, structural and optical properties a series of ~100 nm thick ALD-ZnO films were deposited on a-and c-Al2O3 substrates at 6 different growth temperatures ranging from 100 to 300oC. The films are found to be polycrystalline with average crystallites sizes of ~10-80 nm which increased slightly after Rapid thermal process (RTP) to ~40-120 nm. An increase in the semipolar orientation [101] is observed for ZnO films grown on a- respect to c-Al2O3 with an exception for the ~160-250degC growth window where both polarities compete regardless of the substrate chosen. The RTP was found beneficial for reducing the unwanted polarity as well as for improving the overall structural characteristics (strain, micro-strain, and dislocation density). SIMS and RT-Hall measurements performed on the as grown and annealed films indicate no polarity effects on the inclusion of unintended impurities (H, C, and N) and a similar trend in the resistivity changes, respectively. Acknowledgements. The work has been performed within the National Science Centre projects No. 2018/31/B/ST3/03576 and UMO-2016/22/E/ST3/00553. [1] Waltereit, P., et al. Nature 406.6798 (2000): 865-868.

Authors : Takuma Kato, Shuto Arinaga, Yuki Shimizu, Atuya Hujiwara, Hirohisa Taguchi
Affiliations : Chukyo University Department of Electrical and Electronic Engineering School of Engineering 2-101,Yagoto-Honmachi, Showa Ward, Nagoya City, Aichi Pref., Japan 4668666

Resume : GaN is popularly known to be one of the wide-bandgap semiconductor materials and has been strongly expected to be used in high-breakdown-voltage and high-power electronic devices. In particular, AlGaN/GaN-based high-electron-mobility transistor (HEMT) structures can fully benefit from the wide-bandgap advantages of GaN, so they are attracting attention as next-generation power devices that can help realize mobile communications and an energy-saving society using high-output, high-speed field-effect transistors. However, large quantities of electron traps that form defect levels exist in the AlGaN and GaN layers in the GaN crystal system. The AlGaN/GaN-based HEMTs are prone to the “current collapse phenomenon” in which the electrons in the channel are captured by the traps to increase the ON resistance. In addition, the basic properties of such crystal defects need to be studied in depth. In this study, the drain electrode side was examined for a 10 MHz to 10 GHz frequency sweep using a vector network analyzer in the operating state of the AlGaN/GaN-based HEMT, with simultaneous measurement of the fluctuation of the drain current with respect to frequency variations. Thus, it was confirmed that the current collapse phenomenon occurs below a specific frequency while being suppressed above this value. When a radio frequency is used to sweep the drain side of the AlGaN/GaN-based HEMT, the electric field near the drain electrode gradually accelerates the electrons arriving at the drain with increasing frequency. During this time, some of the channel electrons in the low-frequency region are attracted to the level energies of the crystal defects before their speed increases by the sweep frequency effect; therefore, they are trapped by the crystal defects to cause the current collapse phenomenon. However, the electron velocity increases above a specific frequency, and the channel movement time is reduced compared with the time constant required for the electrons to be trapped in the crystal defect levels. Therefore, the channel electrons can reach the drain region without being trapped by the crystal defects. This indicates that the crystal defects determine the channel carrier trapping based on the frequency. Previous studies have only qualitatively shown that the channel electrons are not trapped by high frequencies and that the current collapse phenomenon can be thus suppressed; however, this study clarifies the frequency response characteristics of the crystal defects.

Authors : Shuto Arinaga,Takuma Kato,Yuki Shimizu,Atsuya Fujiwara,Hirohisa Taguchi
Affiliations : Chukyo University Department of Electrical and Electronic Engneering School of Engineering 2-101,Yagoto-Honmachi,Showa Ward,Nagoya City,Aichi Pref.,Japan 4668666

Resume : Ultraviolet photodetectors are widely used in the biomedical field, as flame sensors, and for ultraviolet photolithography. Ultraviolet rays have extremely high energies owing to their wavelengths, and their effects on the human body cannot be denied. Further, their usage is limited; hence, ultraviolet-light-receiving elements are indispensable when using ultraviolet rays. However, the light-receiving elements are easily damaged by the influence of the ultraviolet radiation. To ensure sufficient strength and durability against ultraviolet rays, photodetectors made of wide-bandgap semiconductors, such as GaN and AlGaN, have been studied. Most of the currently utilized ultraviolet-light-receiving devices are composed of a combination of a pin diode and an amplifier. The pin diode receives the ultraviolet rays, and the amplification mechanism magnifies the output signal. However, the amplification mechanism and light-receiving element are manufactured by separate processes, and each device forming step requires subsequent assembly steps. Therefore, we propose an optical receiver fabricated from AlGaN/GaN-based high-electron-mobility transistors (HEMTs) as both photodetectors and amplifiers. Such photodetectors and amplifiers made of the same material can be fabricated on a single substrate simultaneously. Moreover, even if the received signals are weak, amplification and speeding up can be easily realized by the two-dimensional electron gas of the HEMTs. To confirm the performance of the AlGaN/GaN-based HEMT device as a photodetector, it was irradiated with ultraviolet light of wavelength 370 nm corresponding to the bandgap of GaN, and the light-receiving characteristics were measured. The expected results were confirmed in the form of an increase in the drain current in the linear region of the field-effect transistor compared with the measurements without ultraviolet irradiation. From this increase in drain current, it is considered that light absorption occurs in the GaN layer to generate carriers, which is detected as current amplification. Thus, it is considered possible to realize an optical receiver using the AlGaN/GaN-based HEMT as a photodetector that reacts to ultraviolet wavelengths and have a HEMT structure.

Authors : A. Adhikari, A. Lysak, A. Wierzbicka, P. Sybilski, B. Witkowski, E. Przezdziecka
Affiliations : Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland

Resume : Compound materials formed from group II-VI semiconductor oxides are promising candidates for electronics applications. A unique combination of high exciton binding energy and a wide range of bandgap tunability is a great technological advantage to make use of these materials in optoelectronics. From these group-II-VI oxides, CdO is one of the oldest transparent conducting oxides (TCOs) used for the fabrication of many photovoltaic applications. However, a low bandgap of CdO, which is 2.3 eV (at the ambient condition), restricts its use only in the visible range of application. On the other hand, MgO, which is a direct bandgap semiconductor oxide having a bandgap of 7.8 eV can be alloyed with CdO to make the device used for light emission over UV to Visible regime. A recent report by Przezdziecka et. al. suggests that the bandgap of CdO/MgO superlattice structures(SLs) can be tuned from 2.6 eV to 6 eV by varying the thickness of monolayer in SLs. In this work we have studied Cd1-xMgxO alloy deposited on c- and m- oriented sapphire substrates using plasma-assisted MBE technique. MBE is an epitaxial growth technique in which, the thermal equilibrium has made it possible to overcome the natural solubility limit of these two ternary oxides. Introducing Mg into CdO results in interesting properties to observe in compositional graded Cd1-xMgxO alloys. The concentration of Mg dopant was varied from 0 to 96%. Structural investigation of these alloys was carried out using X-ray diffraction technique. It is observed that with an increase in Mg2 dopant in CdMgO alloys, the lattice constant decreases. The content of Cd and Mg in the alloys was determined using the Energy-dispersive X-ray spectroscopy (EDX) technique. The optical properties of thin films were investigated by UV-Vis spectroscopy at room temperature. From the absorption curve, the optical bandgaps were determined and it was found that the bandgap of films changes from 2.6 eV to 5.6 eV with varying Mg concentration. Using the Modified Vegard’s law, the calculated lattice parameters were fitted with Cd concentration, and the bowing constants were found to be -0.1003 and -0.0826 nm for CdMgO alloys on c- and m-plane sapphire substrate respectively. From the negative bowing value, we can say that the interaction between O-2p and Cd-3d is repulsive. We have studied the influence of Cd-rich to Mg-rich conditions. These results suggest that CdMgO alloys can be a promising material for deep UV light emission and /or detection applications.

Authors : Y. Syryanyy (1), M. Zając (2), E. Guziewicz (3), R. Ratajczak (4) and I.N. Demchenko (1)
Affiliations : (1) University of Warsaw, Department of Chemistry, Pasteura 1 Str., 02-093, Warsaw, Poland; (2) Solaris National Synchrotron Radiation Centre, ul. Czerwone Maki 98, 30-392 Kraków; (3) Institute of Physics, Polish Academy of Sciences, Lotnikow Alley 32/46, 02-668, Warsaw, Poland; (4) National Centre for Nuclear Research, A. Soltana 7, 05-400, Otwock-Swierk, Poland;

Resume : The electronic structure of ZnO:Yb epitaxial layers grown on GaN/sapphire substrates was studied using X-ray absorption spectroscopy at the Zn L3,O K and Yb M5 edges at Solaris light source. Knowing that the ZnO crystallizes in an anisotropic wurtzite structure, the linear polarization of synchrotron radiation was exploited to estimate the influence of the crystal structure anisotropy on the distribution of the local density of states at the site of Zn and O. The calculated partial density of states describes the observed anisotropy in the measured spectra. Influence of the core–hole effect on the analyzed absorption spectra was verified. Acknowledgements: These research took place at the National Synchrotron Radiation Centre SOLARIS, at the PEEM/XAS beamline. The experiment was performed thanks to collaboration of the SOLARIS Team. The work was partially supported by the Interdisciplinary Centre for Mathematical and Computational Modelling (ICM) at University of Warsaw, Poland, grant ID G59-20. The samples growth was co-financed by international project supported bythe Polish Ministry of Science and Higher Education (3846/HZDR/2018/0) and Helmholtz-Zentrum Dresden-Rossendorf (17000941-ST).

Authors : A. Lysak, E. Przeździecka, R. Jakiela, A. Reszka, A. Kozanecki
Affiliations : Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, Warsaw, Poland

Resume : Zinc oxide (ZnO) due to its direct wide bandgap and high exciton binding energy has significant potential in many applications. To expand the functionality of ZnO-based devices, solid alloys can be used. Therefore, the study of the physical properties of up to now poorly tested Zn1-xCdxO solid solutions is justified. Synthesis of Zn1−xCdxO alloys is possible by various methods and we propose to grow quasi ternary alloys based on short period superlattices. In this work we present the results of investigation of quasi ternary alloys in the form of {ZnO/CdO}m short-period superlattices (SLs) with varying layers thicknesses. The structures were grown on (10-10) m-plane sapphire substrate (Al2O3) by molecular beam epitaxy method (MBE). To study the thermal stability of the structures the SLs were annealed for 5 minutes in an O2 environment at a temperature of 900 °C. The chemical composition and interface morphology of as-grown and annealed SLs were examined by Secondary-Ion Mass Spectrometry (SIMS), Scanning Electron Microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX) and Atomic Force Microscope (AFM). The Cd concentration in as-grown SLs varies from 46% to 7.3%, depending on the structure design. The high quality of the as grown SLs is evidenced by the XRD study and low RMS value within 0.238 - 2.29 nm. Upon annealing in oxygen, the properties of {CdO/ZnO}m SLs were studied again. SIMS measurements showed that structural deformation of the SLs takes place. In particular, the SL structure is entirely destroyed, because of diffusion of Cd atoms. It results in a significant decrease of average Cd content in the samples. Also, the SIMS plots revealed an inhomogeneous depth distribution of cadmium. For a more detailed analysis of the Cd distribution with depth, the low temperature (~ 5 K) cathodoluminescence spectra (CL) were collected from different sample depths (~20, 70, 200 and 400 nm). The CL reveals a redshif of about 4 - 60 meV with depth and strongly depends on the structure, namely on Cd contents. The CL spectra reflect the Cd profiles measured with SIMS. Based on the analysis of SIMS and CL data, it was found that the lower the Cd content in as-grown {ZnO/CdO}m SLs, the more uniform the distribution of cadmium over the depth profile after annealing. This work was supported by the Polish National Science Center under Grant No. 2019/35/B/ST8/01937

Authors : Tomoya Nakayama(1), Kotaro Ito(1), Bei Ma(1), Daisuke Iida(2), Kazuhiro Ohkawa(2), and Yoshihiro Ishitani(1)
Affiliations : (1) Graduate School of Electrical and Electronic Engineering, Chiba University, Japan (2) Computer, Electrical and Mathematical Sciences and Engineering Division, King Abdullah University of Science and Technology, Saudi Arabia

Resume : Thermally nonequilibrium phonons generated by the operation of light-emitting devices and transistors deteriorate their operation properties. For example, the population distribution in excitonic states shifts to higher energy levels with low radiation rate, and electrons in the channel of a transistor are scattered leading to the decrease in electron velocity and a further increase in the resistivity. In addition to the device design by electronic viewpoint, thermal energy control is desired, where phonon transport analysis in bulk and heterostructures are required. Previously, thermoreflectance and Raman thermography are investigated. However, separation of heating position and temperature probing position is required to analyze the phonon transport through heterointerfaces. The effects of crystal defects on thermal energy transport have been extensively discussed in many articles. However, microscopic local imaging of heat transport at a specific defect is still a challenge. In Raman measurements, mode-separated information of phonons can be obtained, which is an advantage compared with the pumpprobe method of photo reflectivity. In this paper, we will show the phonon transport analysis by simultaneous irradiation of two laser beams, where the phonon generation and temperature probing are conducted by two lasers. GaxIn1-xN(100nm)/GaN(3m) heterostructures were grown on sapphire substrates by metalorganic vapor phase epitaxy. Two samples with InN mole fraction x of 0.84 and 0.05 were investigated. Microscopic Raman scattering spectroscopy was conducted by selecting a pair of lasers from the wavelength values of 532 nm, 325 nm, and 266 nm. A pair of lasers were incident on samples through an objective lens with NA=0.46 or a reflective objective with NA=0.5. Measurements are performed at room temperature. Raman signals for E2(high) and A1(LO) were obtained. The energy relaxation of generated carriers to the band edges yielded a local heating in a GaInN layer. When the Raman signal of the GaN layer was probed by the 532-nm laser, and the GaInN layer was heated by a UV laser. For the sample of x=0.84, reciprocal space mapping of x-ray diffraction (XRD) analysis showed the partial lattice relaxation. In microscopic PL images, triangle structures originating from dark lines in the regions of high misfit dislocation (MD) density were observed. Raman images of E2(high) mode of the GaN with the heating in the GaInN layer by the 325 nm laser showed the same triangle structure observed in the PL image. The temperature increase in the region with lower PL intensity was lower, which indicates the phonon transport blocking in the vicinity of misfit dislocations. The average temperature increase was estimated to be approximately 50-60 K. On the other hand, for the sample with x=0.05, which shows pseudo morphological growth in the XRD analysis, no triangle structures were observed in PL or Raman imaging. The temperature increase was less than 20 K. This result indicates the higher dissipation of heat energy or phonons in crystals with higher quality. It was found that the lateral phono transport is decayed to a half of the maximum at the position of 10 m from the heating position. These results indicate the Raman imaging using double lasers is effective to analyze phonon transport        through heterointerfaces and to lateral direction inside layers.

Authors : H.Arslan, I.Aulika, A. Šarakovskis, M.Zubkins, L.Bikše, J. Gabrusenoks, J.Purāns
Affiliations : Institute of Solid State Physics, University of Latvia

Resume : Sesquioxides of rare earth elements with +3 ion as Y2O3, Eu2O3, and Lu2O3 are well known for their high optical excitation threshold. An experimental investigation was conducted to explore divalent (+2) yttrium in solid phase in the scope of this research. We produced nanocrystalline-amorphous semiconducting YO thin film at 623 K (± 5) utilizing reactive DC magnetron sputtering. XRD and TEM measurements reveal that the formation of yttrium monoxide is accompanied by the crystalline Y2O3 and Y. In addition to this, spectroscopic investigations such as ellipsometry and XPS and temperature-dependent resistivity measurement denote the semiconducting yttrium oxide has the dominant formation character over Y and Y2O3. The results presented here may facilitate improvements in understanding the oxidation dynamics of rare earth elements, which has a key role in todays and future technology.

Authors : Saszet, K.*(1)(2), Groza, D. (3), Halmagyi, S. (3), Almási, E. E. (4), Pap, Zs.(2)(5)(6), Baia, L. (1)(2)(6)
Affiliations : (1) Faculty of Physics, Babeș–Bolyai University, Mihail Kogălniceanu str. 1, 400084 Cluj–Napoca, Romania; (2) Centre of Nanostructured Materials and Bio-Nano Interfaces, Institute for Interdisciplinary Research on Bio-Nano-Sciences, Treboniu Laurian str. 42, 400271 Cluj-Napoca, Romania; (3) Faculty of Chemistry and Chemical Engineering, Babeș–Bolyai University, Arany János str. 11, 400028 Cluj–Napoca, Romania; (4) Vulcano Research Group, Department of Mineralogy, Geochemistry and Petrology, University of Szeged, Egyetem str. 2, HU-6722 Szeged, Hungary; (5) Department of Applied and Environmental Chemistry, Faculty of Science and Informatics, University of Szeged, Rerrich Béla sqr. 1, HU-6720 Szeged, Hungary; (6) Institute of Research-Development-Innovation in Applied Natural Sciences, Babeș-Bolyai University, Fântânele str. 30, Cluj-Napoca, 400294, Romania; *

Resume : The present study compares two types of TiO2 and magnetic particle (TiO2/MP) composites, based on the source of the MP component and how that influences the structural proprieties of the composites and their applicability on the field of heteorgeneous photocatalysis. As the base photocatalyst of the composite in both cases TiO2 anatase nanoparticles were chosen, TiO2 being a widely researched semiconductor with good photocatalytic properties and easy controllability of size and shape during synthesis. Starting from titanium isopropoxide (TIP) precursor, ethanol and acetic acid, the TiO2 nanoparticles were synthesized using a modified sol-gel hydrothermal method, in a stainless steel autoclave, on 180 °C. The magnetic component of the composites had two fundamentally different sources: one originated from natural magnetic sand, the other was synthetic. In order to prepare the TiO2/natural magnetic particle (TiO2/N-MP) composites, natural sand with magnetic properties was collected from the streambed of a tributary of river Olt (Brașov county, Romania), and processed by micro grinding in a planetary ball mill to an optimal particle size. The as obtained N-MP was introduced in the TiO2 synthesis at the very first step, to obtain composites of N-MP with TiO2 anatase hydrolyzed on their surface. In the case of TiO2/synthetic magnetic particle (TiO2/S-MP) composites a mixture of magnetite (Fe3O4) and maghemite (γ–Fe2O3) iron oxide nanoparticles were synthesized via a simple precipitation method, using FeCl2.4H2O as precursor. The TiO2/S-MP composites were prepared with the same method, as the TiO2/N-MP, except using the synthetic iron oxide nanoparticles. The composition, the crystal structure, the size, the morphology and the optical properties of all the components and both TiO2/N-MP and TiO2/S-MP composites were characterized employing X-ray diffraction, Scanning Electron Microscopy, Raman spectroscopy and Diffuse reflectance spectroscopy. Beside the structural properties and the stability of the composites, their photocatalytic properties were also studied, under UV-A irradiation for the removal of methyl orange (MO) dye and paracetamol from aqueous solution, with promising results. In order to investigate the influence of the MP source on the photocatalytic activity of the composites, the results were also compared with the photocatalytic effieciency of pure anatase TiO2. Acknowledgements.This work was supported by the PN-III-P1-1.1-TE-2019-1318-project. K. Saszet acknowledges the financial support of the Collegium Talentum scholarship provided by the Sapientia Hungariae Foundation.

Authors : Dróżdż P. A.*(1), Kachorovskii V.(1, 2, 3), Prystawko P.(1) , Słowikowski M.(1, 4), Filipiak M. (1, 4), Yavorski D. (1, 5), Szoła M. (1, 5) & Knap W. (1)
Affiliations : (1) CENTERA Laboratories, Institute of High Pressure Physics PAS, Warsaw, Poland (2) Ioffe Institute, St. Petersburg, Russia (3) Rensselaer Polytechnic Institute, Troy, New York, USA (4) CEZAMAT, Warsaw University of Technology, Warsaw, Poland (5) Faculty of Physics, University of Warsaw, Warsaw, Poland

Resume : The Inverse Faraday Effect (IFE) - the appearance of stationary magnetic moments magnetization caused by circulary polarized light - has been mostly studied in magnetic materials. Recently, the IFE was predicted in the periodic lattice of metallic disks or spheres placed the vicinity of two dimensional electron liquid and subjected to the external circularly polarized radiation. The radiation causes the DC current loops in the electron liquids, thus leading to appearance of static magnetic moments. Physically, the interaction between metal disks and two dimensional electron liquid, the "twisted" plasmonic modes are excited which lead (due to rectification) to appearance of DC circulating current In this work, we present the basic idea of IFE enhanced by twisted plasmons. The mechanism of the effect is described and the theoretical predictions are presented. The GaN/AlGaN is proposed as a basic system for the experimental realization of the IFE. In order to observe IFE experimentally, the GaN/AlGaN HEMT like structure was prepared with 2 dimensional electron gas as a channel. On top of the structure, the periodic lattice of metal disks were fabricated with use of electron beam lithography. In addition, the frequency of twisted plasmonic modes can be slightly tuned with use of conducting back - gate layer that is present in epitaxial structure. We present the theoretical predictions and the technological realization of the structure as well as its basic characterization.

Authors : S.V. Nikiforov1, G. Akhmetova-Abdik2, A. Dauletbekova2, Zh. Karipbayev2, S. Zvonarev1, D. Ananchenko1, M. Zdorovets1,3
Affiliations : 1Ural Federal University, 19, Mira Str., Yekaterinburg, Russia 2L.N. Gumilyov Eurasian National University,2 Satpayev Str., Nur-Sultan, Kazakhstan 3The Institute of Nuclear Physics’ Astana branch,2/1 Abylaikhan Ave., Nur-Sultan, Kazakhstan

Resume : Zirconium dioxide of various phase composition, widely used in modern technology, should have high stability of characteristics under various radiation effects. This is especially important when used in military and space technology, as well as in the nuclear industry. The determining factor influencing the stability of the luminescence properties of oxide dielectrics under irradiation is the formation of radiation-induced defects in the anion sublattice (oxygen vacancies). Investigation of the effect of the size of nanoparticles, doping in the synthesis of micro- and nanostructured compacts and ceramics based on ZrO2 is necessary to predict and increase the radiation resistance, as well as to elucidate the nature of the intrinsic luminescence of ZrO2, which has not yet been finally established [1-3]. Micro- and nanostructured compacts were prepared by uniaxial cold pressing of monoclinic ZrO2 nanopowder and tested using SEM (Carl Zeiss Sigma VP), and X-ray fluorescent analysis. The compacts were irradiated by 130 keV and 10 MeV electrons (Linear Electron RADAN Accelerator, LERA-10-10C, Yekaterinburg, Russia) and 200 MeV Xe ions (cyclotron DC-60, Nur-Sultan, Kazakhstan). Thermostimulated luminescence (TSL) of irradiated samples showed the presence of different peaks. A number of TSL peaks have been identified. The kinetic parameters of the TSL were also calculated. References 1. C. Barry Carter, M. Grant Norton. Ceramic Materials. Science and Engineering. Springer, 2007. 716 p. 2. Salari, S., and F.E. Ghodsi. Journal of Luminescence 182 (2017): 289-299. 3. Aleksanyan E., Kirm, M., Feldbach, E., & Harutyunyan, V. Radiation Measurements 90 (2016): 84-89. Keywords: zirconium dioxide, electron beam, swift heavy ions, thermostimulated luminescence, kinetic parameters.

Authors : M. Mamatova1, V. Skuratov2, 3, A. Olejniczak2,4, A. Dauletbekova1, A. Akilbekov1, Sh. Giniyatova1
Affiliations : 1 L.N. Gumilyov Eurasian National University, 2 Satpayev Str., Nur-Sultan, Kazakhstan 2 2Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, 6 Joliot-Curie Str., Dubna, Russia 3National Research Nuclear University MEPHI, 31 Kashirskoe shoosse, Moscow, Russia 4Faculty of Chemistry, Nicolaus Copernicus University, 7 Gagarina Str., Torun, Poland

Resume : Among the many oxides, aluminum-magnesium spinel MgAl2O4 is one of the most radiation-resistant dielectric materials that are promising for use in nuclear power devices. [1]. At present, most of experimental studies about radiation defects in spinel were received using high-energy electrons, neutrons, and low energy ions [2, 3]. The aim of this work is to study radiation defects in MgAl2O4 irradiated with swift heavy ions using picosecond pulsed photoluminescence. Spinel single crystals were irradiated with 710 MeV Bi, 167 MeV Xe, 107 MeV Kr and 46 MeV Ar ions up to the fluence 2·1013 сm-2 at IC-100 and U-400 cyclotrons (Dubna, Russia). The photoluminescence spectra excited by picosecond laser source (wavelength 445 nm, pulse duration FWHM < 80 ps) have been measured at room temperature using the confocal microscope Integra Spectra, NT-MDT. It was shown that the PPL spectra from unirradiated MgAl2O4 contain sharp lines with a maximum at 1.8 eV related to emission of Cr3+ ions and a band at 2.35 eV, which is assigned to Mn2+ ions. As a result of irradiation with high energy Kr ions, a broad emission band appears at 1.7 – 2.5 eV (500 – 750 nm), which indicates the radiation origin of the corresponding luminescence centers. Similar bands were observed in the PPL spectra of MgAl2O4 irradiated with Bi, Ar and Xe ions. It was found that radiative lifetimes equal 8 ns, 8.9 ns, 12.3 ns and 13.7 ns for the emission wavelength 500 nm, 520 nm, 620 nm and 650 nm, respectively. References: 1. S.S. Raj, S.K. Gupta, V. Grover, K.P. Muthe, V. Natarajan, A.K. Tyagi. Journal of Molecular Structure 2015; 1089: 81-85. 2. A. Lushchik, E. Feldbach, E.A. Kotomin, I. Kudryavtseva, V.N. Kuzovkov, A.I. Popov, V. Seeman, E. Shablonin. Scientific reports, nature search 2020; 10: 1-9. 3. E. Feldbach, I. Kudryavtseva, K. Mizohata, G. Preditis, J. Raisanen, E. Shablonin, A. Lushchik Optical Materials 2019; 96: 1-7. Keywords: aluminum-magnesium spinel MgAl2O4, swift heavy ions, pulsed photoluminescence, radiation defects.

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Applications : Chairs: Cesare Franchini
Authors : Tadeusz Suski, Katarzyna Pieniak, Grzegorz Muziol
Affiliations : Institute of High Pressure Physics, PAS, UNIPRESS, Warsaw, Poland

Resume : It is well known fact that InGaN/GaN based light-emitting diodes (LEDs) and laser diodes (LDs) suffer from the high built-in electric field in their quantum wells (QWs). The common observation is that the nitride emitters with wider QWs and higher In-content in the QWs are more sensitive to the this obstacle. The related effect known as Quantum Confined Stark Effect (CQSE) results from spatial separation of the electron and hole wave function, reduction of their wave-function overlap and strong red-shift of the emission energy. Moreover, intensity of luminescence is strongly reduced. On the other hand, increase of the driving current ID, required for reasonable light emission leads to screening of the QCSE. The arising shift of the emission energy, EEM, is commonly used as a monitor of the screening efficiency. Saturation of EEM at high IDs is interpreted as the entire elimination of the built-in electric field. In this presentation we demonstrate results of the application the high pressure method to determine the amount of internal electric field remaining or eliminated entirely from the quantum wells of studied LEDs and LDs. The most important questions we answer in this work are: i) how efficient is the screening of the internal electric field of polar InGaN/GaN emitters by carriers injected by driving current; ii) to what extent is the efficiency of this screening dependent on the construction of the studied LEDs and LDs, in particular on the thickness and the amount of Indium in the QWs composing InGaN/GaN emitters.

Authors : Balagula, R.M.*(1), Subačius, L.(1), Jorudas, J.(1), Prystawko, P.(2), & Kašalynas, I(1).
Affiliations : (1)Center for Physical Sciences and Technology, Vilnius, LT-10257, Lithuania; (2)Institute of High Pressure Physics PAS, Warsaw, 01-142, Poland

Resume : Different methods are being considered to realize tunable solid-state sources of terahertz (THz) radiation. We propose using a transit-time resonance phenomenon in polar semiconductors. The effect manifests as a periodic movement of electrons in reciprocal space under strong electric field resulting in modulation of current density and modification of electron distribution function. Emission of radiation with wavelength defined by phonon energy and tuned by electric field strength was earlier demonstrated in InP crystals at sub-THz frequency range. In the present work we developed a 10 μm-thick n-type GaN epilayers on a native semi-insulating substrate for high-voltage and high-frequency (up to THz) applications. Hall experiments show electron mobility of 1000 cm2/V⋅s and concentration of 1⋅1016 cm-3 at 300 K. We analyze conductivity characteristics under nanosecond voltage pulses up to 1 kV and optical transmission spectra from sub-THz to IR spectral ranges. The impurity breakdown followed by a nonlinear mobility dependence on applied electric field observed in current-voltage characteristics obtained at different temperatures down to 77 K are discussed. Then, field-induced fast change in transmission of THz beam at different wavelengths polarized either along or orthogonally to the applied electric field is presented. Moreover, the work indicates new practical possibilities of polar wide band gap materials controlled by strong electric field amplitude.

Authors : Ahmad Sauffi Yusof (a,b), Sidi Ould Saad Hamady (a), Christyves Chevallier (a), Nicolas Fressengeas (a), Zainuriah Hassan (b), Sha Shiong Ng (b), Mohd Anas Ahmad (b), Way Foong Lim (b)
Affiliations : (a) Université de Lorraine, CentraleSupélec, Laboratoire Matériaux Optiques, Photonique et Systèmes (LMOPS), F-57000 Metz, France; (b) Universiti Sains Malaysia, Institute of Nano Optoelectronics Research and Technology (INOR), 11800 USM, Penang, Malaysia

Resume : Among the III-V semiconductors (including III-Nitride), InGaN is the only material that provides an excellent spectral match with the solar spectrum. In addition, the absorption coefficient of InGaN is much higher compared to any other III-V materials, thus making it possible to be used for thin-film solar cells. InGaN also has high carrier mobilities, high resistance to extreme conditions (temperature and ionizing radiation) and very high chemical stability. The combination of these favorable properties leads InGaN to be the subject of intense research work in the realization of high-efficiency solar cells. The work in this area has been focused on addressing the main technological challenges, primarily on the difficulty of producing monocrystalline InGaN epilayers with a high indium composition, the p-doping issue and the difficulty to realize high-quality metal contacts. In order to achieve better crystal quality and reduce defect density, InGaN is typically grown heteroepitaxially on unintentionally or intentionally doped GaN templates. Thus, it allows the development of the elaboration and optimization process to be carried out, which is suitable for photovoltaic application in the typical transverse structures. However, in this structure configuration, the electronic and structural properties of the grown InGaN epilayer are known to be strongly dependent on the substrate and the growth conditions. The electronic properties of an active layer grown on a semiconducting substrate are particularly difficult to investigate using a typical electrical characterization method such as Hall effect with van der Pauw configuration. This is due to the transport parameters obtained from the electrical characterization are mainly originating from the underlying thick semiconducting GaN template. Thus, to overcome this limitation, we proposed for the first time a two-layer-based model methodology to investigate the transport properties of the InGaN epilayer grown in such structure configuration. Through this route, the electrical properties of the InGaN epilayers can be precisely extracted from the experimental data of the van der Pauw and Hall effect measurement. The procedure was applied to perform an in-depth study of the transport properties of InGaN epilayer with respect to indium composition ranging from 4 % up to 18 %. The electrical measurements were performed with temperatures ranging from 20 K up to 350 K. The effect of metal-organic chemical vapor deposition (MOCVD) growth conditions and electrical measurement temperature on the variation of the carrier concentration and mobility were discussed with respect to the X-ray diffraction, Raman spectroscopy and atomic force microscopy results. The developed code and other related data of the two-layer model analysis for the van der Pauw and Hall effect experimental data will be made available, which can be easily adapted to other materials where the active layer is grown on a semiconducting substrate.

Authors : Quang Minh Thai, Sergi Cuesta, Lou Denaix, Sylvain Hermelin, Olivier Boisron, Stephen T. Purcell, Le Si Dang, Eva Monroy,
Affiliations : Institut Lumière Matière, CNRS, University of Lyon, University Claude Bernard Lyon 1, F-69622 Villeurbanne, France; University Grenoble-Alpes, CEA, Grenoble INP, IRIG, PHELIQS, F-38000 Grenoble, France; University Grenoble-Alpes, CEA, Grenoble INP, IRIG, PHELIQS, F-38000 Grenoble, France; Institut Lumière Matière, CNRS, University of Lyon, University Claude Bernard Lyon 1, F-69622 Villeurbanne, France; Institut Lumière Matière, CNRS, University of Lyon, University Claude Bernard Lyon 1, F-69622 Villeurbanne, France; Institut Lumière Matière, CNRS, University of Lyon, University Claude Bernard Lyon 1, F-69622 Villeurbanne, France; University Grenoble-Alpes, CNRS, Institut Néel, F-38000 Grenoble, France; University Grenoble-Alpes, CEA, Grenoble INP, IRIG, PHELIQS, F-38000 Grenoble, France;

Resume : The requirement of a low resistivity p-AlGaN contact layers still presents a technological hurdle for the development of highly efficient electrically injected UV light emitters. Recently, cathodo-pumping with a high-energy electron beam was proposed as a novel approach to inject electrons into the active optical gain layer. Such devices do not require doping and are not sensitive to the asymmetric mobility of electrons and holes. First experimental demonstration showed a maximum lasing temperature of 107 K at 355 nm [1]. Further characterization is necessary to understand the performance and achieve cathodo-pumped lasing at room temperature. Here, we report gain measurements at room temperature of 10 pairs of Al0.07Ga0.93N/GaN multi-quantum wells (MQWs) contained in a separate confinement heterostructure, designed for cathodo-pumping [2], with similar MQWs structure compared to Ref. [1]. We used the variable stripe length method, with a 193 nm ArF excimer laser as pump source. Depending on the probed area of the sample, the net gain threshold varies between 220 and 410, with net gain reaching up to 131 cm-1 and 240 cm-1 at 740 Combined with the intrinsic electron-hole generation efficiency limit of cathodo-pumping, we predict a lower limit for cathodo-pumped lasing threshold at room temperature of 660 for this structure. [1] T. Hayashi et al., Scientific Reports 7, 2017. [2] S. Cuesta et al., Optics Express 29 (9), 2021.

Authors : Sébastien Leroy, Redouane Douali, Christian Legrand, Freddy Krasinski, Florent Blanchard, Pascal Roussel, Sébastien Saitzek, Jean-François Blach
Affiliations : Univ. Artois, CNRS, Centrale Lille, Univ. Lille, UMR 8181, Unité de Catalyse et Chimie du Solide (UCCS), F-62300 Lens, France ; ULCO, Unité de Dynamique et Structure des Matériaux Moléculaires (UDSMM) EA 4476, F-62100 Calais, France ; ULCO, Unité de Dynamique et Structure des Matériaux Moléculaires (UDSMM) EA 4476, F-62100 Calais, France ; ULCO, Unité de Dynamique et Structure des Matériaux Moléculaires (UDSMM) EA 4476, F-62100 Calais, France ; Univ. Lille, CNRS, Centrale Lille, Univ. Artois, UMR 8181, Unité de Catalyse et Chimie du Solide (UCCS), F-59000 Lille, France ; Univ. Lille, CNRS, Centrale Lille, Univ. Artois, UMR 8181, Unité de Catalyse et Chimie du Solide (UCCS), F-59000 Lille, France ; Univ. Artois, CNRS, Centrale Lille, Univ. Lille, UMR 8181, Unité de Catalyse et Chimie du Solide (UCCS), F-62300 Lens, France ; Univ. Artois, CNRS, Centrale Lille, Univ. Lille, UMR 8181, Unité de Catalyse et Chimie du Solide (UCCS), F-62300 Lens, France

Resume : Oxide materials have been extensively studied these last years for many applications as ferroelectric memories, piezoelectric actuators, solar cells, luminescence, water splitting. Among them, layered perovskites and especially, rare earth titanates with chemical formula Ln2Ti2O7 (Ln = rare earth) reveal interesting properties and are promising candidates for photovoltaic devices. In addition, for the applications cited below, the knowledge of the transport properties is fundamental. In this goal, we present the electrical characterizations of La2Ti2O7 thin films synthetized by pulsed laser ablation. Firstly, we note a significant change in I-V curve in the presence of UV light. The conduction mechanism in this material is explained and can be described by two regimes: ohmic at low voltage and space charge limited conduction for higher voltage. Secondly, for the first time at our knowledge, the charge carrier mobility of this material is studied; we use the time of flight method to investigate this property. We analyze the evolution of the photocurrent and the carrier mobility with the applied voltage by the presence of a depletion layer between the film and the gold contact which affects the measurements.

10:00 Live Questions & Answers session 5    
10:30 Break    
Engineering Materials I : Chairs: John Buckeridge
Authors : Chris G. Van de Walle
Affiliations : Materials Department, University of California, Santa Barbara, California, USA

Resume : Ga2O3 is a highly promising material for power electronics, thanks to its large band gap (4.8 eV) and high breakdown voltage. Better control of doping is still an active research topic, both in Ga2O3 and in (AlxGa1-x)2O3 alloys. In Ga2O3, the identity of a secondary donor with a larger ionization energy (~100 meV) is still elusive. In alloys, controlled doping at low concentrations has proven difficult, and native-defect compensation and DX-center formation limit doping at higher Al concentrations. First-principles modeling, using advanced hybrid functional calculations within density functional theory, can greatly help in resolving experimental puzzles and guiding optimal doping conditions. I will discuss a recently developed methodology that allows accurate calculations of ionization energies, and show how it can help resolve the experimental observations. I will also elaborate on compensation mechanisms in (AlxGa1-x)2O3 alloys. Finally, I will address acceptor doping aimed at producing material in which the Fermi level is pinned far from the band edges. Work performed in collaboration with S. Mu, J. L. Lyons, H. Peelaers, J. B. Varley, M. Wang, and D. Wickramaratne.

Authors : Abou Daher, M.*(1), Lesecq, M.(1), García-Sánchez, S.(2), Íñiguez-de-la-Torre, I.(3), Pérez, S.(3), Lingaparthi, R.(4), Nethaji, D.(4), Radhakrishnan, K.(4), González, T.(3), Mateos, J.(3), Gaquiere, C.(1)
Affiliations : (1) Institute of Electronics, Microelectronics and Nanotechnology (IEMN), France (2) Department of Physics and Mathematics, University of Alcalá de Henares, Madrid, Spain (3) Department of Applied Physics, University of Salamanca, Salamanca, Spain (4) Nanyang Technological University, Singapore * lead presenter

Resume : With the aim of developing electronic applications reaching THz frequencies, room temperature compact and possibly tunable solid-state sources must be developed. The most common approach is to apply the frequency multiplication concept to a GHz frequency fundamental RF source, for example Gunn diodes (GDs). In this work we explore the development of GaN GDs, which due to its wide band gap, high saturation velocity and short energy relaxation time, can potentially operate at much higher frequencies (above 300 GHz) and provide much higher power than traditional GaAs GDs. In this work, we report on our efforts on the simulation, fabrication and characterization of GaN planar GDs to realize a THz fundamental oscillator based on Gunn effect using tapered nanochannels. This geometry benefits the appearance of Gunn oscillations since it is able, first, to focus the electric field at the cathode side of the channel, and, second, reduce the huge DC power necessary to reach the threshold field of GaN (above 100 kV/cm), and avoid burning the devices. Another important novelty of our technology is the use of a thin and highly doped GaN epilayer as active material instead of a AlGaN/GaN heterostructure. We will report on the simulation of the optimum epilayer and device parameters, the growth of high quality material, the development of the technology for fabricating the tapered nanochannel topology, and, finally, to the characterization of the devices, which is now in progress.

Authors : Wrana, D.*(1,2), Rodenbücher, C.(3), Gensch, T.(4), Cieślik, K.(1), Jany, B.R.(1), Szot, K.(5), Setvin, M.(2), & Krok, F.(1)
Affiliations : (1) Marian Smoluchowski Institute of Physics, Jagiellonian University, Krakow, Poland (2) Department of Surface and Plasma Science, Charles University, Praha, Czechia (3) Institute of Energy and Climate Research (IEK-14), Forschungszentrum Jülich, Jülich, Germany (4) Institute of Biological Information Processing 1 (IBI-1), Forschungszentrum Jülich, Jülich, Germany (5) August Chelkowski Institute of Physics, Silesian Univerisity, Katowice, Poland

Resume : Many widely used nanomaterials are based on transition metal oxides (TMOs), not only because of their abundance but also due to the remarkable ease of tuning of their properties via reduction-oxidation processes. During such, the density of oxygen vacancies is tuned, contributing to the substantial changes in the electronic and structural properties and tailoring them to meet specific needs e.g. in (photo)catalysis, energy production, and storage. In this presentation, the impact of thermal reduction on the surface and bulk properties of two wide-bandgap oxide materials, TiO2 and SrTiO3, will be presented. Reduction of both crystals results in the formation of oxygen vacancies and therefore d-electrons, which leads to changes in the work function and a rise in electrical conductivity, which could be tuned over many orders of magnitude [1]. A new SPM-based technique, combining LC-AFM and KPFM, allows probing the same area of reduced oxide surfaces [2], helping to understand the nanoscale resistive switching. Besides the change in electrical properties, the surface structure evolves towards nonstoichiometric reconstructions [1], due to the increased oxygen deficiency. Not only the carrier concentration and bandgap states are affected but simultaneously exciton lifetimes extend, as measured by the two-photon fluorescence microscopy [3]. Such reduction-based effects are especially interesting with regards to the catalytic performance of metal oxide-based nanostructures. Surprisingly, not only is oxygen flow possible during UHV annealing of the oxide crystal but also incongruent cation sublimation can be triggered, as demonstrated for the perovskite oxides like SrTiO3 [4]. Extremely low oxygen partial pressure (ELOP), achieved by the use of an oxygen-getter, initiates SrTiO3 crystal decomposition and the formation of stable monocrystalline cubic TiO nanowires with a c(4x4) reconstructed surface [5]. Such bottom-up growth of conductive TiO nanostructures could be an alternative to other costly methods, resulting in the creation of the TiO/SrTiO3 interface, with a sharp transition between Ti2+ and Ti4+ states, proven by atomically-resolved electron microscopy. This oxide heterostructure provides an interesting metal/semiconductor junction with a 0.6 eV work function difference [6], opening many new possibilities for (photo)catalysis and aiding in the search for exotic interface states. ELOP process appears also as a general mechanism, where nanostructures of desired density and height could be formed on other perovskite oxide surfaces. [1] Wrana, D. et al. (2018) Applied Surface Science, 432, 46-52. [2] Rodenbücher, C. et al. (2018) APL Materials, 6(6), 066105. [3] Wrana, D. et al. (2021), Applied Surface Science, accepted [4] Rodenbücher, C. et al. (2017) physica status solidi (RRL)–Rapid Research Letters, 11(9), 1700222. [5] Wrana, D. et al. (2019) Nanoscale, 11(1), 89-97. [6] Wrana, D. et al. (2019) Beilstein journal of nanotechnology, 10(1), 1596-1607.

Authors : A. Regoutz
Affiliations : Department of Chemistry, University College London, London WC1H 0AJ, UK.

Resume : Ga2O3 is an ultra-wide band gap oxide material, which promises great improvements in a range of applications, including power electronics, solar blind UV photodetectors, and gas sensing devices. Its high conductivity, high breakdown field, and large band gap have led to a flurry of research in the past few years. Most of the work has focused on its most stable form, monoclinic β-Ga2O3. However, Ga2O3 presents pronounced polymorphism and a number of other polymorphs beyond β exist, including hexagonal α-Ga2O3, cubic γ-Ga2O3¬, and orthorhombic ε-Ga2O3. Although this wealth of possible structures opens up opportunities to control and tune structure, electronic structure and ultimately physical characteristics, the polymorphs beyond β-Ga2O3 are comparatively unexplored. Here, we present an in-depth study of the electronic structure of the α, β, and ε polymorphs of Ga2O3. The samples investigated are either bulk single crystals or epitaxial films grown using molecular beam epitaxy (MBE) or atomic layer deposition (ALD), selecting the highest quality samples available for each of the polymorphs. We report high-resolution valence bands from hard and soft X-ray photoelectron spectroscopy (SXPS and HAXPES) which are directly compared to theoretical partial and total electronic densities of states as calculated within the framework of density functional theory (DFT). Both deep and shallow core level spectra are compared to DFT results to explore the influence of structure, rather than solely the oxidation state, on the core level behaviour. X-ray absorption spectroscopy (XAS) is used to probe the unoccupied states and in combination with SXPS is used to gain an estimate of the changes in the band gaps of the polymorphs. Ultimately, this work presents a systematic and comprehensive study of the electronic structure of Ga2O3 polymorphs, providing an insight into electronic trends and their relationship to crystal structure. This comparative study helps to discern trends between the different structures and advances our understanding of this polymorphic material. It lays the foundation for further exploration of Ga2O3 in applications beyond its β phase.

Authors : Soumen Mandal1, Karsten Arts2, Harm Knoops2,3, Jerome Cuenca1, Georgina Klemencic1, Oliver A. Williams1
Affiliations : 1School of Physics and Astronomy, Cardiff University, Cardiff, UK 2Eindhoven University of Technology, 5612 AZ Eindhoven, Netherlands 3Oxford Instruments Plasma Technology, North End, Yatton, Bristol, BS49 4AP, UK

Resume : The study of growth of large gallium oxide substrates is an on-going topic, researchers have already demonstrated devices made from gallium oxide. The devices point towards promising advantages in gallium oxide over traditional wide band gap semiconductors like SiC and GaN. However, as with most high-power devices, thermal management in gallium oxide devices, with its low thermal conductivity (10-30 W/mK), is a major bottle neck in the development of technology based on this material. A potential solution to the thermal management problem can be to grow a diamond layer on gallium oxide single crystal[1]. To grow diamond on any non-diamond substrate, a seeding or nucleation step is essential. In this work we have determined the zeta potential of gallium oxide single crystal using the streaming potential method. The zeta potential was found to be negative in the pH range of 6-7. So, a positively charged diamond solution[2] was used to seed the gallium oxide surface. The seeded wafers were introduced in chemical vapour deposition system for growth of diamond. It was found that the gallium oxide surface dissociated on contact with the diamond growth plasma. To overcome this problem the gallium oxide surface was coated with ~100nm aluminium oxide and silicon dioxide using plasma-assisted atomic layer deposition. Zeta potential of the ALD layers were determined to select the diamond seed solution. The seeding and growth process were repeated on the coated surfaces. While silicon dioxide surfaces proved to be effective in protecting the gallium oxide surface, aluminium oxide layers were etched away in the growth plasma. The grown layers were characterised using Raman spectroscopy and scanning electron microscopy. The thin diamond films were found to be heavily stressed and as a result only thin layers could be grown on gallium oxide. References 1 S. Mandal et al. Carbon, 181, 79 (2021) 2 S. Mandal, RSC Adv. 11, 10159 (2021).

12:30 Live Questions & Answers session 6    
13:00 Break    
Computational Methods and Advanced Characterization : Chairs: Tim Veal
Authors : Cesare Franchini
Affiliations : CMP - Quantum Materials Modelling University of Vienna Kolingasse 14-16/03.65, A-1090 Vienna, AUSTRIA

Resume : Polarons are quasiparticles that can form in polarizable materials by entanglement between charge carriers and lattice distortions. Polaron defects are ubiquitous, strongly influence material properties and play an important role in many processes involving carrier mobility and charge transfer [1]. One of the most characteristic manifestations of the polaron is the formation of additional states within the gap of insulating and semiconducting compounds, localized or dispersive bands depending on the spatial extension of the polaron wavefunction. In this talk, we shall discuss the computational modeling of polarons using first principles methods also combined with machine learning techniques, providing examples on different types of polarons (surface polarons, bipolarons, magnetic and Jahn-Teller polarons) and various polaron-induced phenomena (polaron-adsorbate interaction, polaron-induced surface reconstructions, polaron-spin couplings). [1] Franchini, C., Reticcioli, M., Setvin, M. et al. Polarons in materials. Nat Rev Mater (2021). DOI:10.1038/s41578-021-00289-w

Authors : José Villafuerte*(1-2), Odette Chaix-Pluchery(1), Joseph Kioseoglou(3), Fabrice Donatini(2), Eirini Sarigiannidou(1), Julien Pernot (2), Vincent Consonni (1)
Affiliations : (1) Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, F-38000 Grenoble, France; (2) Univ. Grenoble Alpes, CNRS, Grenoble INP, Institut NEEL, F-38000 Grenoble, France; (3) Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece; * lead presenter

Resume : Controlling the physical properties of ZnO nanowires (NWs) grown by chemical bath deposition (CBD) is crucial for their piezoelectric application. However, their growth occurs in a medium containing impurities such as carbon, nitrogen and hydrogen. It’s been shown that the hydrogen in bond-centered sites (HBC) and zinc vacancy – hydrogen (VZn-3H) complexes act as two shallow donors with very low formation energy.1 Additionally, N related defects also play a significant role on the physical properties of ZnO NWs.2 In particular, we showed by density-functional theory that the VZn-NO-H defect complex acts as a deep acceptor with a relatively low formation energy and exhibits a Raman line at 3078 cm-1 along with a red-orange emission energy of around 1.82 eV in cathodoluminescence spectroscopy. The nature and concentration of these defects were engineered as a function of annealing temperature under oxygen atmosphere. ZnO NWs annealed at 300 °C under oxygen atmosphere specifically exhibits a reduction of the free charge carrier density from 10.2 x 1017 to 5.6 x 1017 cm-3 along with a high mobility of about 60 cm2/V.s assessed by longitudinal optical phonon – plasmon coupling analysis. These findings further reveal that the engineering of the N- and H-related defects, as the major source of crystal defects in ZnO NWs grown by CBD, is capital for obtaining the high resistivity required to avoid the piezoelectric potential screening by free charge carriers in the related piezoelectric devices.3 1. Villafuerte, J. et al. Zinc Vacancy–Hydrogen Complexes as Major Defects in ZnO Nanowires Grown by Chemical Bath Deposition. J. Phys. Chem. C 124, 16652–16662 (2020). 2. Villafuerte, J. et al. Engineering nitrogen- and hydrogen-related defects in ZnO nanowires using thermal annealing. Phys. Rev. Mater. 5, 056001 (2021). 3. Gao, Y. & Wang, Z. L. Equilibrium potential of free charge carriers in a bent piezoelectric semiconductive nanowire. Nano Lett. 9, 1103–1110 (2009).

Authors : Jaime Dolado, Ruth Martínez-Casado, Pedro Hidalgo, Bianchi Méndez
Affiliations : Departamento de Física de Materiales, Universidad Complutense de Madrid, E-28040 Madrid, Spain

Resume : Zinc germanate oxide is an emerging wide band gap (Eg = 4.5 eV) semiconductor of great interest in optoelectronics, photocatalysis and energy storage applications. The optical properties of undoped Zn2GeO4 are commanded by the native point defects, which bring about to several several luminescence bands in the ultraviolet-visible region [1,2]. Besides native defects, it is well known that impurities also play a role in electronic and optical properties, due to the electronic levels introduced in the band gap. For instance, Li doping leads to changes in the morphological and electrical properties of ZnO nanostructures [3]. In this work, the effects of Li doping in Zn2GeO4 microrods have been analyzed, which have not been reported until now. The microstructures were grown by thermal evaporation method, using a ZnO:Ge precursor mixture, to which Li2CO3 was added in different concentrations. The detailed morphological, compositional and structural characterization showed a good crystalline quality of the Li doped Zn2GeO4 microrods. Significant changes were observed in the morphology of the samples obtained depending on the Li2CO3 concentration added to the precursor mixture. An in-depth study of the luminescent features of the microrods was carried out by cathodoluminescence (CL) and photoluminescence (PL) techniques. These measurements revealed the existence of different emissions ranging from visible to UV, being the blue emission the dominant at room temperature. A study of integrated PL intensity as a function of temperature revealed that the blue emission exhibited an anomalous behaviour, called negative thermal quenching (NTQ), as the PL intensity increased with increasing temperature. This NTQ was not observed in the undoped sample, supporting that Li doping has significant effects on luminescence of Zn2GeO4. In addition, Density Functional Theory (DFT) calculations were performed to simulate the electronic states within the bandgap generated by the incorporation of Li into the Zn2GeO4 lattice both as an interstitial position and as replacing Zn (LiZn). The DFT results showed that LiZn leads to the formation of an acceptor state within the band gap similar to that caused by the Zn vacancy defect. Therefore, the incorporation of Li enhances the efficiency of the visible emission of Zn2GeO4 at room temperature, making the microstructures obtained in this work potential candidates for use as visible light LEDs. [1] P. Hidalgo et al. “Synthesis and optical properties of Zn2GeO4 microrods” Acta Materialia 104, 84-90 (2016) [2] J. Dolado et al. “Understanding the UV luminescence of zinc germanate: the role of native defects” Acta Materialia 196, 626-634 (2020) [3] R. Bhattacharjee and I-M Hung. “Effect of different concentration Li-doping on the morphology, defect and photovoltaic performance of Li–ZnO nanofibers in the dye-sensitized solar cells”. In: Materials Chemistry and Physics 143.2 (2014), pp. 693–701.

Authors : Masaya Chizaki, Kensuke Oki, and Yoshihiro Ishitani
Affiliations : Graduate School of Electrical and Electronic Engineering, Chiba University, Japan

Resume : 1S exciton is the main luminescence source in electron-hole systems because their radiative recombination rate is higher than that of free carriers or excitons with a higher principal quantum number. The density of nonradiative recombination centers (NRC) is now decreasing by the improvement of crystal quality, and the internal quantum efficiency of the radiation is increasing. However, in the ultraviolet emission region, it is reported that the radiative efficiency decreases with the shortening of the emission wavelength of AlGaN. In these crystals with NRC, high radiative recombination rate is an advantage to increase the internal quantum efficiency of the radiation. In experimental research, the radiative recombination lifetime of exciton has been measured by the photoluminescence method for the bulk GaN. Among various results on the temperature dependence of the radiative recombination lifetime of the 1S exciton, some report the dependence proportional to the power 3/2 of temperature. This temperature dependence of the radiative recombination lifetime has been considered to be theoretically acceptable for bulk materials, whereas this scheme is valid only when we assume the localization of excitons in the 1S state under a thermal equilibrium condition of kinetic energy. However, this assumption is questionable because it has been reported that the population is distributed to the states of the free carriers and the excitons with various principal quantum numbers. On the other hand, the values of the power greater or less than 3/2 have also been experimentally reported. At present, the mechanism yielding these various temperature dependences of the radiative recombination lifetime has not been cleared. We have constructed the phononic-excitonic-radiative (PXR) model, including the exciton states with the principal quantum number up to five, continuum states, and various elementary processes based on phononic, electron-collisional, and radiative mechanism, which include the interaction of excitons with various phonons. Using this PXR model, greater power of temperature than 3/2 is expected for ideal crystals of undoped GaN. In the present report, we introduce the effects of background electrons and the energy broadening to our PXR model, and show the mechanism to yield various values of the power of temperature. Our calculation reveals that the density of background electrons regulates the population flows of excitation and deexcitation, and that the share of the population in the lower principal quantum number state increases gradually as the increase in temperature because of the gradual reduction of the number of effective states by the increase in the energy broadening and exciton scattering. It is expected that the temperature dependence depends on crystal quality from the viewpoint of electron density and the ratio of the broadening energy and exciton binding energy.

Authors : Kwok C. K. G.* (1), Yu K. M. (1)
Affiliations : (1) Department of Physics, City University of Hong Kong

Resume : Valence bands (VBs) of most transition metal oxides (TMOs) are deriving from O 2p states that give rise to relatively flat dispersion and lie rather low with respect to vacuum level. Hence achieving p-type conductivity for TMOs is a formidable task. The shortage of reliable p-type wide gap TMOs hinders the advancement of transparent electronic devices. Tin monoxide (SnO) has an alleviated localized VB states due to strong hybridization of the Sn 5s2 and O 2p orbitals from the proximities of their energy levels, and thus can exhibit p-type conductivity with a higher hole mobility. With its wide bandgap of ~2.8 eV, SnO becomes a promising candidate as a p-transparent layer for photovoltaics and optoelectronic devices. Nominally undoped SnO can achieve a high hole concentration of ~10^18 cm^-3 due to the low formation energy of Sn vacancies (VSn) acceptors. However, SnO is metastable that tend to be converted to n-type SnO2, making the synthesis of stable p-type SnO still challenging. In this work, we attempt to enhance the p-type conductivity of SnO via the manipulation of the VSn acceptor concentration. O stoichiometry in SnO was controlled by co-sputtering of Sn and SnO targets followed by post-growth rapid thermal annealing (RTA) in a temperature range of 300-500oC. We found that pure phase SnO with tetragonal structure exhibiting high p-type conductivity can be obtained by SnO films grown with tiny additional Sn RTA at 300oC in N2. Films with hole concentration in the range of 10^18-10^19 cm^-3 with relatively high hole mobility of 1-6 cm^2/Vs are achieved. These films exhibit optical transparency of 30-60% in visible range. Prospect of improving the p-type conductivity of SnO with extrinsic acceptor doping by Ga and Na will be discussed.

15:30 Live Questions & Answers session 7    
16:00 Break    
Authors : Bryan Horcholle(a), Christophe Labbé(a), Xavier Portier(a), Philippe Marie(a), Clara Grygiel(a), Cédric Frilay(a), Sylvain Duprey(a), R. Daou(b) , Wojciech Jadwisienczak(c), David Ingram(d) ,Julien Cardin(a)
Affiliations : (a) CIMAP Normandie Université, ENSICAEN, UNICAEN, CEA, CNRS, 6 Boulevard Maréchal Juin, 14050 Caen Cedex 4, France; (b) CRISMAT Normandie Université, ENSICAEN, UNICAEN, CNRS, 6 Boulevard Maréchal Juin, 14050 Caen Cedex 4, France; (c) School of Electrical Engineering and Computer Science, Ohio University, Athens, Ohio 45701, USA; (d) Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, USA

Resume : Niobium pentoxide Nb2O5 is a stable1 dielectric material with direct band gap that found numerous of application in several modern technologies as corrosion resistant material1, catalysis2, or electronic application (memristor3). Moreover, due do its high refractive index n and low extinction coefficient k on visible range between 400nm to 1200nm, Nb2O5 have numerous potential applications in photonic technologies4. The combination/alternation with a low refractive material allows a strong contrast necessary for making optical filters or waveguides. Nb2O5 thin films were grown on Si (100) P type wafer by rf magnetron sputtering under pure argon atmosphere with 2?? diameter Nb2O5 99.95% pure target. These films were then annealed by rapid thermal annealing at different temperatures (Ta) ranging from 400°C to 1000°C. Elemental analysis was performed by means of RBS. Microstructural investigations were made thanks to XRD and TEM measurements. The energy dispersion of n(E) and k(E) over UV-VIS-NIR spectral range was investigated by means of two complementary techniques: spectroscopic ellipsometry based on polarization measurement and spectrophotometry based on intensity measurement. Both measurement were analyzed thanks to Tauc-Lorentz dispersion model. Experimental uncertainties on n(E) and k(E) were obtained by a Monte Carlo re-sampling technique of the Tauc-Lorentz model parameters. Stable Nb2O5 films on Si substrate were obtained from room temperature (RT) to 900°C, higher Ta (1000°C) results in a film destruction. The films stoichiometry was found conform to Nb2O5 over the full range RT to 900°C. Nb2O5 films were found amorphous from RT to 500°C, crystallized in pseudohexagonal phase at 600°C and in the orthorhombic phase from 700°C to 900°C. Thanks to error estimation, we found that n(E) and k(E) results of both experimental methods are consistent. The n(E) and k(E) evolution with Ta showed different behaviors: (i) from RT to 400°C and at 900°C, high k(E) values in VIS range appeared which differs from Nb2O55 optical quality (ii) from 400°C to 800°C, low k(E) values were found which is consistent with optical quality Nb2O5. Moreover, on the 400°C to 800°C range, the band gap energy was found decreasing from 3.44eV down to 3.04eV. This last behavior is attributed to a film densification of thin films with the increase of annealing temperature concomitant with phase?s modifications. All observed structural and optical properties of Nb2O5 thin films were consistent, showing the possibility to get high quality stable stoichiometric amorphous or polycrystalline Nb2O5 film that might be integrate in optical structure such as broadband filters. 1. C.Nico et al, ?Progress in Materials Science? (2016) 2. N. Hara et al., Journal of the Electrochemical Society 141, no. 6 (1994): 1669. 3. T. Ushikubo, Catalysis Today 57, no. 3?4 (2000): 331?38. 4. M. Fredell et al. International Society for Optics and Photonics, 2017 5. F. Lemarchand, private communications (2013)

Authors : H.D.T. Nguyen1,2, D. Zhang1, T. M. Nguyen3, and J. Seidel1,2
Affiliations : 1 School of Materials Science and Engineering, UNSW Australia, Sydney, Australia 2 ARC Centre of Excellence in Future Low Energy Electronics Technologies (FLEET), UNSW Australia, Sydney, NSW 2052, Australia 3 School of Physics, UNSW Australia, Sydney, Australia

Resume : Topotactic transitions, i.e. reversible crystal structure changes due to controllable stoichiometry of material, offer the substantial potential to control a wide variety of functionality in transition metal oxides, especially in systems with high ionic mobility and correlated electrons. The topotactic phase transition in epitaxial perovskite (PV) and brownmillerite (BM) SrCo0.67Fe0.33O3−δ (SCFO) thin films grown by pulsed laser deposition is investigated by detailed X-ray diffraction, conductive AFM, SQUID magnetometry, and optical measurements with regard to structural, electronic, magnetic, and optical properties. The material exhibits weak magnetic properties up to room temperature and an additional clear ferromagnetic transition near 50 K. The topotactic phase transition between PV and BM phases can be controlled by wet-chemical etching, thermal energy through a redox reaction, or applying different bias voltages. We also report on topotactic electrochromism with prominent coloration efficiency (CE) in SrCo0.66Fe0.34O3-δ observed associated with changes in the material's electrical conductivity and electronic structure. Our results show that changes in electron correlation lead to significant coloration and light absorption, which provides a general approach for utilizing topotactic transitions in electrochromic applications.

Authors : Vincenzo Vinciguerra*(1), Antonio Landi (2), Herbert Hintermaier (3), Paolo Badalà (4), Gerald Klug (5), Alessandro Sitta (6), Michele Calabretta (7), Anna Bassi (8), Marco Renna (9), Angelo Alberto Messina (10)
Affiliations : (1) Automotive & Discrete Group R&D, STMicroelectronics, Italy; (2) Automotive & Discrete Group R&D, STMicroelectronics, Italy; (3) DISCO Hi-Tec Europe GmbH, Germany; (4) Analog & Power Front End Manufacturing, STMicroelectronics, Italy; (5) DISCO Hi-Tec Europe GmbH, Germany; (6) Automotive & Discrete Group R&D, STMicroelectronics, Italy; (7) Automotive & Discrete Group R&D, STMicroelectronics, Italy; (8) Analog & Power Front End Manufacturing, STMicroelectronics, Italy; (9) Automotive & Discrete Group R&D, STMicroelectronics, Italy; (10) Italy Public Affairs, STMicroelectronics, Italy.

Resume : Imperfections in silicon carbide (SiC) die can have an impact on their mechanical properties, affecting the target of the high reliability standard required in power devices intended for automotive applications. In this work the failure strength of 4H-SiC square die of different thicknesses has been determined through a ball-on-ring (BOR) test and compared with previous three-point bending test results. Moreover, an interpretation of the experimental results on the net deflection δ-δ0 at the center of the die sample, according to a revisited Vitman and Pukh equation, has been reported. This allowed to achieve an assessment of the effective or equivalent Young’s modulus of the die, with the BOR equipment on back-grinded 4H-SiC die, thinned up to 110 μm. The BOR provided consistent values for the 180 μm thin samples with the results from the previous the 3-PB test and a value of the equivalent Young’s modulus of (391 ± 90) GPa for the 110 μm, which is comparable with the theoretical limit measured in 4H-SiC.

Authors : Getaneh D. Gesesse (a), Olivier Debieu (a,b), Aline Jolivet (a), Cedric Frilay (a), Philippe Marie (a), Christophe Labbé (a), Mohamad El-Roz (c), and Julien Cardin (a)
Affiliations : (a) CIMAP Normandie Université, ENSICAEN, UNICAEN, CEA, CNRS, 6 Boulevard Maréchal Juin, 14050 Caen Cedex 4, France; (b) Cirimat, 4 allée Emile Monso, BP-44362, 31030 Toulouse Cedex 4, France; (c) Laboratoire Catalyse et Spectrochimie, CNRS, ENSICAEN, Université de Caen, 6 Boulevard Maréchal Juin 14050, Caen cedex, France

Resume : Transparent conductive oxides (TCO) are important groups of materials that combine high optical transparency with high electrical conductivity. Wide bandgap (Eg >3 eV) metal oxides are the main candidates for TCO due to their good optical transparency in the visible range and their high charge carrier densities significantly increased by doping. In this context, the objective of this work is to synthesis Nb doped anatase TiO2 (TiO2:Nb) thin films by atomic layer deposition (ALD) technique followed by annealing. This deposition technique was chosen due to its ability to produce high quality layers of targeted stoichiometry, with controllable thickness and sharp interfaces with a low thermal budget. Films are produced with parameters in the shared deposition window of TiO2 and NbOx using Titanium (IV) isopropoxide (TTIP) and Niobium (V) ethoxide (NEO) as precursors, and water as oxidizing agent. Various TiO2:Nb films are synthesized with variable Nb contents at two different deposition temperatures (Td) with the aim to control the growth rate, the structure and the morphology, that influence the optical features and the electrical conductivity. The dopant content is tuned by the ratio (RNb) of the number of NEO cycles over the total number of ALD cycles. In order to investigate the characteristics of the TiO2:Nb films deposited on Si wafers and glass substrates, various techniques are used as spectroscopic ellipsometry, spectrophotometry, XRD, Raman, FTIR, SEM, AFM, and four probe resistivity. In this communication, 46-nm thick TiO2 films deposited at Td=200 and 300 °C, are respectively amorphous and polycrystalline anatase. These two deposition conditions are used in the aim of producing efficient Nb-doped anatase TCO using subsequent annealing. For the 300 °C-as-deposited TiO2:Nb films, the growth rates show almost similar behavior as the pure TiO2 film, at a very low RNb from 0.005 to 0.05. The Raman and XRD results show that these films keep the crystalline anatase phase. Those observations are confirmed by FTIR spectra, which interestingly reveal new peaks attributed to Nb doping effect. However, as the RNb reaches 0.1, the growth rate drastically drops and the films become concomitantly amorphous similarly to our as-deposited NbOx. At 1.95 eV, the refractive index of the 300 °C-as-deposited films varies as a function of RNb concomitantly with this phase and composition evolution. It is closed to the anatase one of 2.50 for low RNb, while it rises to values comparable with amorphous TiO2 at RNb = 0.1 and progressively decreases to the one of our NbOx ~2.35 with further increase of RNb. The annealing at different temperature (400-800 °C) under N2 atmosphere of the 300 °C-films improves and converts into anatase thin films produced with 0.1 < RNb < 0.33. Subsequently, we will present the similar study at Td=200 °C of the as-deposited TiO2:Nb, compare the two approaches, and investigate the annealing effect on the optical and electrical properties of the films.

Authors : Lukasz Wachnicki, Sylwia Gieraltowska, Bartlomiej S. Witkowski, Elzbieta Guziewicz
Affiliations : Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland

Resume : Ti-based films are extensively studied as a prospective material due to UV-protection, antibacterial and effective photocatalyst properties. Ti-based materials such as TiO2 show relatively high reactivity and chemical stability under ultraviolet light (λ<387nm), whose energy exceeds the band gap of 3.3 eV in the anatase crystalline phase. The development of photocatalysts exhibiting high reactivity under visible light (λ> 400 nm) should allow the main part of the solar spectrum, even under poor illumination of interior lighting, to be used. In this work, we show the obtainment of Ti-based films with different chemical compositions using the atomic layer deposition (ALD) method. These layers were prepared using chemical reactions of between two of listed precursors: H2O, TiCl4, TiN4(CH3)2 and Al2(CH3)6. Modification of the composition of Ti-based layers allows deposition of materials with quite different structural, optical and electrical properties. The optimized Ti-based films with mixed composition will be discussed. Photoluminescence (PL), X-ray diffraction (XRD), atomic force microscope (AFM) and scanning electron microscope (SEM) measurement will be presented.

Authors : A. Karg (1), M. Kracht (2), N. Braud (1), J. Schörmann (2), M. Rohnke (3), P. Vogt (1), J. Janek (3), J. Falta (1), M. Eickhoff (1)
Affiliations : (1) Institute of Solid-State Physics, University Bremen, Otto-Hahn-Allee 1, 28359 Bremen (2) Institute of Experimental Physics I and Centre of Material Research (LAMA), Justus Liebig University Gießen, Heinrich-Buff-Ring 16, 35392 Gießen, Germany (3) Institute of Physical Chemistry, Justus Liebig University Gießen, Heinrich-Buff-Ring 16, 35392 Gießen, Germany

Resume : The molecular beam epitaxy (MBE) of the wide bandgap semiconductor Ga2O3 bears unique challenges during the growth process. These are not only low growth rates in general, but also the formation and desorption of volatile suboxides resulting in a decreasing growth rate with increasing Gallium-flux until the layer growth is completely suppressed. This behavior contrasts with the MBE growth of e.g., GaAs, GaN or ZnO. It was found by Kracht et al.[1] and Vogt et al.[2] that the additional supply of Sn and In as catalysts lead to an enhanced growth rate in the metal-rich regime, as these materials form an additional oxygen reservoir, enabling higher growth rates and an extension of the growth window as well as the stabilization of the metastable e-Ga2O3 polymorph. The fundamental understanding of this metal-catalyzed molecular beam epitaxy is still an open question of current research. We present a detailed study on the Sn-catalyzed growth of Ga2O3 by MBE. In contrast to former studies the amount of the used catalyst was reduced from permanent Sn supply to the deposition of a SnO2 delta-layer in the initial state of growth, which catalyzes the growth of Ga2O3 film of several hundred nanometers. We propose that the Sn provided by the decomposition of the SnO2 delta-layer by Ga adatoms floats on the growth surface, acting as a catalytic adlayer, and resulting in an enhanced catalytic action. By various analysis techniques such as XPS, ToF-SIMS, HRXRD and AFM the presence and distribution of the catalyst layer during different growth stages as well as its impact on the grown Ga2O3 layers were studied. [1] Kracht et al., Phys. Rev. Appl. 8, 054002 (2017) [2] P. Vogt, Ph.D. thesis, Humboldt University, Berlin, Germany (2017)

Authors : E. Guziewicz1, W. Wozniak1, S. Mishra1, R. Jakiela1, M. Guziewicz2, V. Yu. Ivanov1, E.Lusakowska1, R. Schifano1
Affiliations : 1Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, PL-02 668 Warsaw, Poland 2Research Network Łukasiewicz - Institute of Electron Technology, Aleja Lotników 32/46, PL 02 668 Warsaw, Poland

Resume : Electrical properties of semiconducting ZnO are of vital importance, because they determine the successful application of this material in micro- and optoelectronics. High electron concentrations, which are widely observed in undoped ZnO, are generally believed to be closely related to the hydrogen impurity, which directly, as interstitial hydrogen, or indirectly, as hydrogen-native defect complexes, influences the material conductivity [1]. In the present work the origin of hydrogen in polycrystalline ZnO films grown by thermal Atomic Layer Deposition was investigated by comparing layers deposited using H2O and 2H2O as oxygen precursor, while diethylzinc was used as zinc precursor. The series of ZnO-ALD films with 220-270 nm thickness were grown at 100, 130 and 200oC. Secondary Ion Mass Spectroscopy measurements of the as grown and 800 oC annealed films provide evidence that the hydrogen contribution originating from the oxygen precursor is weakly chemically bound and can be mostly removed by rapid thermal annealing performed at 800oC [2]. On the other hand, the remaining hydrogen introduced by carboxyl groups originating from the metalorganic zinc precursor withstands such treatment. Considering that in the annealed samples the hydrogen and carbon content are similar, this possibly indicates that at least part of the residual hydrogen might be in the form of –CH complexes. Acknowledgements. The work has been performed within the National Science Centre projects No. 2018/31/B/ST3/03576 and UMO-2016/22/E/ST3/00553. [1] Y. K. Frodason, K. M. Johansen, T. S. Bjorheim, B. G. Svensson, and A. Alkauskas, Phys. Rev. B 2018, 97, 104109 [2] E. Guziewicz, W. Wozniak, S. Mishra, R. Jakiela, M. Guziewicz, V. Yu. Ivanov, E. Lusakowska, R. Schifano, Phys. Stat. Sol. A 2021, 218, 2000318

Authors : Chukova O., Nedilko S.A., Nedilko S.G., Voitenko T.
Affiliations : Taras Shevchenko National University of Kyiv, Volodymyrska Str., 64/13, Kyiv 01601, Ukraine

Resume : Glass-ceramics based on oxide composite materials are promising for applications in luminescent converting coatings for light emitting devices. These glass-ceramics were characterized by high thermal and mechanical stabilities. Development of such glass composites in in this work was carried out using vanadate nanoparticles incorporated into vanadate-borate glass matrices. The samples were made by the melt quenching method from boron acid and vanadium pentoxide with adding of some other oxides as modifiers and luminescent vanadate nanoparticles doped with lanthanum. Simultaneous manifestations of both glass and crystalline components in the XRD patterns of the samples have confirmed creation of vanadate-borate glass-ceramics materials. Luminescence properties of the made samples were measured in the wide spectral range. It was found that spectra of the doped with vanadate nanoparticles composites contain narrow spectral lines in the 550 -720 nm spectral range Those lines were ascribed to well-known f-f electron transitions in the RE ions. Influence of conditions of synthesis and optimal ratios of the components those allow obtaining of samples promising for practical applications as luminescent materials are discussed Acknowledgment. The work has received funding from Ministry of Education and Science of Ukraine and from the Horizon Europe research and innovation program within transnational access activity NFFA under grant agreement No 654360.

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13:00 Break    
Engineering Materials II : Chairs: Marco Kirm
Authors : John Buckeridge
Affiliations : School of Engineering - Electrical & Electronic Engineering London South Bank University, 103 Borough Road, London SE1 0AA

Resume : Wide-gap oxides and nitrides form crucial components of modern electronic and optoelectronic devices. As there is a delicate balance between ionic and electronic disorder in these systems, understanding their defect properties is a priority in order to improve device efficiencies. Computational modelling is an essential tool for this task. We focus here on the electronic properties of defects in wide-gap oxides and nitrides, and investigate how compact and diffuse states affect the defect-related properties of these materials. We employ an embedded cluster technique to model defects, and discuss the advantages of this approach and potential pit falls. We calculate intrinsic defect formation energies, ionisation properties and concentrations in typical transparent conducting oxides (In2O3, ZnO and SnO2) and in GaN. Our results help explain experimentally observed trends in those materials. We also study doping in ZnO and GaN, looking at complex formation and determining optical properties of common impurities. Finally, we discuss a classical force field model of defects in In2O3 and SnO2, which may be employed to simulate solid solutions of the two oxides.

Authors : Anastasia V. Glushkova,†,‡ Harold F.W. Dekkers,† Manoj Nag,† Jose Ignacio del Agua Borniquel§a, Jothilingam Ramalingam§b, Jan Genoe,†,‡ Paul Heremans,†,‡ and Cedric Rolin†
Affiliations : †IMEC, Kapeldreef 75, B-3001 Leuven, Belgium; ‡ESAT, Katholieke Universiteit Leuven, B-3001 Leuven, Belgium; §Applied Materials, §aAPTD, Belgium, §bMPD, USA

Resume : In-Ga-Zn oxide (IGZO) is a wide bandgap material beneficial as an active layer in thin-film transistors (TFTs) for integrated circuits, display and imager backplanes due to its low off-current, relatively high mobility, and good uniformity over large substrates. Deposition conditions of two mostly studied phases – amorphous and c-axis-aligned crystalline (CAAC) IGZO – are being optimized to mitigate the main limitation of IGZO TFTs – bias stress instability, but there is an information gap on a side-by-side comparison of both phases. Here we study both IGZO phases and the transition between them – protocrystalline IGZO, defined as amorphous IGZO with an onset of CAAC crystallinity. It evolves to CAAC IGZO with temperature increase and to mixed amorphous + nano/microcrystalline IGZO with oxygen flow ratio and thickness increase at physical vapor deposition. A microstructural study is performed to explain this transition and to link material properties of all three phases to their electrical properties in TFTs. We demonstrate that the highest performance of both amorphous and CAAC IGZO TFTs do not pair with their best stability, while the protocrystalline IGZO has its highest field-effect mobility (13.5±0.5 cm2/Vs) and best stability (down to 0.043±0.022 V after 104 sec under bias stress of 1 MV/cm) at the same deposition conditions. With these results, we aspire to increase understanding of IGZO phases, their material and electrical properties and to promote IGZO applicability.

Authors : M. Stachowicz1, A. Wierzbicka1, J.M. Sjakowski1, M.A. Pietrzyk1, P. Dłużewski1, E. Dynowska1, S. Magalhaes2, E. Alves2, A. Kozanecki1
Affiliations : 1Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46 PL-02-668 Warsaw, Poland 2Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal

Resume : Zinc oxide (ZnO) is attracting a tremendous interest for its numerous potential applications in optoelectronics [1], for it is a wide bandgap semiconductor (3.37 eV at room temperature) with a high exciton binding energy of 60 meV, which can increase in ZnMgO/ZnO/ZnMgO quantum wells (QWs) up to 100 meV or more [2]. Due to the high freeexciton binding energy, excitonic emission processes can persist at room temperature. For epitaxial growth of ZnO related films and quasi-ternary alloys, reducing the strains and dislocations is critical. Thereby closely lattice-matched substrates, which are ZnO substrates, are beneficial for two-dimensional growth and enhanced electric, optical and structural properties [3]. Nevertheless of alluded above advantages of growths on single crystal ZnO substrates, obtaining such ZnO epilayers and ZnO/ZnMgO structures without phase separation is still a challenging issue, especially in the case of non-polar orientations, where crystal quality is still poor. Very few works have reported the growth of a-plane ZnMgO layers until now, and the state-of-the-art random alloys are mainly restricted to low thickness and low Mg content (below 30%) [3]. The use of non-polar ZnO substrates simplifies the analysis of the properties of QS, because they are free of internal electric fields and therefore, the observed processes of exciton recombination are not affected by the quantum-confined Stark effect (QCSE) [3]. The aim of this work is a detailed study of non-polar short period MgO/ZnO SLs grown on a-ZnO bulk crystalline substrates, and to find out how thicknesses of the MgO layers, in the SLs consisting of 30 pairs of thin (1- 2.5 nm) ZnO quantum wells and (1-3 nm) MgO barier layers, correlate to the mean content of Mg, whether possible is retaining of WZ structure, and how it affects forming multi-quantum well structures and theirs PL emission. The detailed structural and optical analysis of subjected ZnO/MgO quasi-ternary alloys in form of superlattices allowed to study the influence of different phases of ZnO and MgO on the interface’s abruptness. We found that the wurtzite structure is retained in the MgO thin barriers up to 2 nm, but some diffusion of Mg from barriers to ZnO QW’s was inevitable as well as the presence of biaxial strains. As a result, a subtle, the size of three monolayers, ZnMgO film is created at the interfaces, which is partly responsible for retaining the wurtzite structure of completely strained MgO layers. Acknowledgements: The project was supported by the Polish National Science Centre (NCN) based on the decision No: DEC-2018/28/C/ST3/00285. [1] M.A. Pietrzyk, M. Stachowicz, et al., Journal of Crystal Growth, 408 (2014) 102-106. [2] H. D. Sun, T. Makino, et. al, Jour. Appl. Phys., 91 (2002) 1993. [3] L. Beaur, T. Bretagnon,et al., Physical Review B, 84 (2011) 16531

Authors : Santanu Ghosh, Preetam Singh, Pushp Sen Satyarthi and Pankaj Srivastava
Affiliations : Nanostech Laboratory, Department of Physics, Indian Institute of Technology Delhi, India

Resume : We have entered in a new age of technology, where the transport of elementary particles will be driven by its spin degree of freedom. A new electronics, which is completely based on 'spin' of electron popularly known as 'Spintronics' is a subject of current research. The basic materials required for such technology is a daunting task to materials scientists. In this work after introducing briefly the motivation of this new technology, we will highlight the research works carried out in last decade related to (i) diluted magnetic semiconductors (DMSs) a basic material for future spintronics and (ii) defect mediated ferromagnetism in WBSs like ZnO and GaN. Ion implantation has been identified as an important tool to synthesize diluted magnetic semiconductor (DMS) materials. Synthesis of transition metal implanted ZnO as a DMS material, and their ferromagnetic properties from intrinsic to extrinsic regime will be discussed. Origin of ferromagnetism (due to substitution of transition metals in ZnO) probed by a combined study of X-ray absorption (XAS), X-ray magnetic circular dichroism (XMCD), X-ray photo electron spectroscopy (XPS), X-ray diffraction (XRD) and SQUID will be highlighted. Finally, N will be discussed. Results will explained in the framework of bound magnetic polaron model (BMP) and density functional theory (DFT).

Authors : Imre Miklós Szilágyi
Affiliations : Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, Hungary

Resume : In the lecture several examples will be shown about how various nanostructured photocatalysts can be obtained by atomic layer deposition (ALD), based on experience of our group. The advantage and disadvantage of ALD films on the photocatalytic activity will be discussed. By combining electrospinning and ALD, Vis or UV active photocatalysts were prepared, e.g. WO3/TiO2, ZnO/TiO2 and TiO2/ZnO core/shell nanofibers, TiO2 nanotubes. By using sol-gel and ALD, SiO2/TiO2 core/shell photocatalytic nanoparticles were obtained. Photocatalysts based on biological substrates were also manufactured by ALD, e.g. TiO2 coated lotus leaves with both superhydrophobic and photocatalytic activities. C60, graphene oxide, polymer and carbon aerogels, carbon nanospheres, PMMA nanoparticles coated with ALD ZnO, TiO2 and Al2O3 oxide layers and particles are examples for carbon and polymer nanostructure based photocatalysts. On the previously mentioned substrates, amorphous and crystalline TiO2, ZnO and Al2O3 thin films were grown by ALD at various temperatures. While TiO2 is considered to have photocatalytic activity only in the crystalline state; unexpectedly, we observed that when TiO2 was deposited in amorphous form on organic and biological substrates, i.e. lotus leaf, C60-OH, GO, graphene oxide or PMMA, the amorphous TiO2 layer clearly exhibited photocatalytic property.

15:30 Live Questions & Answers session 9    
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II-VI Based Materials III : Chairs: Kin Man Yu, Yevgen Melikhov
Authors : Jack E. N. Swallow, Benjamin A. D. Williamson, Thomas J. Featherstone, Joe Willis, David O. Scanlon and Tim D. Veal
Affiliations : Department of Physics and Stephenson Institute for Renewable Energy, University of Liverpool, UK Department of Chemistry, University College London, UK

Resume : Novel transition metal and lanthanide dopants can be used to enhance the properties of transparent conducting oxides (TCOs). Here, the mechanisms behind their superior performance compared with conventional dopants are presented from both experimental and theoretical perspectives. Enhanced electron mobility and infrared transparency are realised by virtue of the electron-donating orbitals being resonant with, but not interacting with, the host material conduction band. As a result, the low band edge electron effective mass of the host metal oxide is retained, which is in stark contrast to the behaviour for conventional doping of TCOs. Comparative case studies are presented of Mo and Ce versus Sn doping of In2O3 [1,2] and Ta versus Sb and F doping of SnO2 [3,4]. Optical, transport, photoemission, and density functional theory results provide evidence of our new mechanistic understanding. [1] J. E. N. Swallow, B. A. D. Williamson, D. O. Scanlon, T. D. Veal et al., Mater. Horiz. 7, 236-243 (2020) [2] T. J. Featherstone, J. Willis, D. O. Scanlon, T. D. Veal et al., unpublished. [3] B. A. D. Williamson, T. J. Featherstone, D. O. Scanlon, T. D. Veal et al., Chem. Mater. 32, 1964-1973 (2020) [4] J. E. N. Swallow, B. A. D. Williamson, D. O. Scanlon, T. D. Veal et al., Adv. Funct. Mater. 28, 1701900 (2018)

Authors : Doina Craciun1, Petronela Garoi1, Marian Mogildea2, George Mogildea2, Sorin I. Zgura2, Bogdan S. Vasile3, Valentin Craciun1, 4
Affiliations : 1National Institute for Laser, Plasma and Radiation Physic, Laser Department, 409 Atomistilor St., PO Box Magurele, Romania;2Institute for Space Science, 077125, Magurele, Romania; 3University "POLITEHNICA" from Bucharest, Faculty of Applied Chemistry and Material Science, Department of Science and Engineering of Oxide Materials and Nanomaterials, Bucharest, Romania; 4Extreme Light Infrastructure for Nuclear Physics, ELI-NP, IFIN-HH, Magurele, Romania

Resume : Single crystal In2O3 nanoparticles were synthesized using microwaves vaporization of metallic In wires in air. The output of an 800 W microwave generator was coupled through an antenna to a cylindrical wave guide cavity with a metallic In wire placed in the electromagnetic node, where a high power density was achieved. The wire strongly absorbed the microwaves, resulting in its heating, vaporization and finally a plasma plume formation. Optical emission spectroscopy investigations indicated that a high electronic temperature was reached in the plasma plume. The vaporized material was collected on a piece of Si placed opposite the wire, near the cavity wall. Scanning electron microscopy investigations showed that the deposited material consisted of an agglomeration of In2O3 nanoparticles. X-ray diffraction and transmission electron microscopy investigations indicated that the nanoparticles were very crystalline, with random orientation. X-ray photoelectron spectroscopy analysis confirmed the formation of stoichiometric In2O3. High resolution TEM investigations found that the nanostructures were single crystals, with faceted surfaces. This simple method could have many applications for metal nanocrystal oxides synthesis. Acknowledgments: This work was supported by a grant of the Ministry of National Education and Scientific Research by project code PN-III-P2-2.1-PED-2019-2949 and Nucleu programme - contract LAPLAS VI, no. 16N/2019.

Authors : Jesús Redondo1, Pavel Kocán1, Giada Franceschi2, Igor Sokolović2, Florian Kraushofer2, Michele Riva2, Gareth S. Parkinson2, Michael Schmid2, Ulrike Diebold2, Martin Setvin1,2
Affiliations : 1) Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic 2) Institute of Applied Physics, TU Wien, Austria

Resume : Polarons strongly influence the catalytic activity of transition metal oxides[1]. The study of polaron formation and dynamics is fundamental to understanding the actual mechanisms and yields of catalytic reactions in these materials. A new method for the investigation of electron and hole polarons is demonstrated. Charge carriers are injected with the AFM tip into natural and Ti-doped α-Fe2O3(1-102). These carriers form a cloud of trapped charges, which expands due to electrostatically and thermally activated polaron hopping. Annealing of the sample and characterization by Kelvin probe force microscopy provides information on polaron dynamics; these results are compared to KMC simulations and the dependence of the hopping activation energy on the Ti doping is shown. [1] M. Reticcioli et al., Phys. Rev. Lett. 122, 016805 (2019)

09:30 Live Questions & Answers session 10    

Symposium organizers

(SMT-ETRC), Rudolf-Eber-Str. 2, 73447 Oberkochen, Germany
Iraida N. DEMCHENKO (main organizer)Warsaw University

Department of Chemistry, ul. Pasteura 1, 02-093 Warsaw, Poland
Yevgen MELIKHOVCardiff University

School of Engineering, Queens Bldg., The Parade, Cardiff, CF24 3AA, Wales, United Kingdom