Wide bandgap semiconductors for LEDs, solar and related energy technologies
Focus is on new emerging material technologies using wide bandgap semiconductors as active material in LEDs, solar cells and related technologies. Novel growth concepts, surface engineering, technology implementation approaches, and conceptual materials combinations are of primary importance.
Traditional materials used for light emitting diodes and solar cells are driving these markets. However, there are profound challenges in energy and environmental savings. New materials approaches will provide complementary technologies to the conventional ones. Novel approaches using wide bandgap semiconductors is an attractive field now when epitaxial and bulk growth is sufficiently developed. Thereby base materials such as SiC and nitrides have matured enough to allow new concepts.
The symposium topic is around SiC and nitrides in LEDs and solar cells, but also addressed to include related wide bandgap materials and applications. The main contributions expected is from research where SiC is an active material (such as optoelectronic and solar devices) beyond traditional substrate or transistor function, and nitrides in deep UV, LD concepts beyond the blue LED.
Hot topics to be covered by the symposium:
Fluorescent SiC for white LED and solar SiC is a growing field which has emerged strongly since 2010. The organizers of this proposed symposium have conducted several national and international projects on these topics. Other research groups now join this exciting arena. The studies in which SiC is a direct active material are in LEDs and solar cells, but also water splitting, CO2 splitting, nanocrystals and other energy and environmental technologies. The combination of SiC and nitrides is of specific relevance since that has shown to successfully introduce high brightness white LEDs in general lighting. Therefore innovative nitride approaches is included as a topic, such as deep UV LEDs, laser diodes, VCSELs.
The papers will be published in Advanced Materials Proceedings (VBRI Press) which has open access and publishes peer-reviewed conference proceedings that reveals a significant advance understanding of latest research and innovations in the field of materials science and technology.
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SiC : Didier Chaussende
Authors : Peter J. WELLMANN
Affiliations : Crystal Growth Lab, Materials Department 6 (i-meet), University of Erlangen (FAU), Martnesstr. 7, 91058, Erlangen, Germany
Resume : The presentation will review the development of SiC bulk growth technology from its early beginning until today’s stat-of-the-art. The first part will describe the physical-chemical fundamentals to grow low defect SiC bulk crystals of the 4H polytype as it is applied in power electronic devices. Critical process parameters to reduce the density of dislocations, secondary inclusion, polytypes inclusions and intentional doping (n-type and p-type) will be discussed. The second part will focus on the growth technology, in-situ growth visualization techniques and challenges of crystal wafering. In the third part current trends to grow SiC for novel optical applications for lighting and solar technologies will be outlined.
Authors : T. A. Nugraha, M. Rohrmueller, U. Gerstmann, S. Greulich-Weber, A. Stellhorn, J. L. Cantin, J. Von Bardeleben, W. G. Schmidt, S. Wippermann
Affiliations : Max-Planck-Institut fuer Eisenforschung; University of Paderborn; University of Paderborn, Solar Weaver GmbH, University of Paderborn, Pierre and Marie Curie University, University of Paderborn, Max-Planck-Institut fuer Eisenforschung
Resume : SiC is widely used in high-power, high-frequency electronic devices. Recently, it has also been employed as a building block in nanocomposites used as light absorbers in solar energy conversion devices. Analogous to Si, SiC features SiO2 as native oxide that can be used for passivation and insulating layers. However, a significant number of defect states are reported to form at SiC/SiO2 interfaces, limiting mobility and increasing recombination of free charge carriers. We investigated the growth of oxide on different 3C-SiC surfaces from first principles. Carbon antisite Csi defects are found to be strongly stabilized in particular at the interface, because carbon changes its hybridization from sp3 in the SiC-bulk to sp3 at the interface, creating a dangling bond inside a porous region of the SiO3 passivating layer. Combining ab initio g-tensor calculations and electron paramagnetic resonance (EPR) measurements, we show that Csi defects explain the measured EPR signatures, while the hyperfine structure allows to obtain local structural information of the oxide layer. Financial support from BMBF NanoMatFutur grant 13N12972 and DFG priority program SPP-1601 is gratefully acknowledged.
Authors : Ondrej Caha (1,2), Maria Losurdo (3), Kurt Hingerl (4), Josef Humlicek (1,2)
Affiliations : (1) Central European Institute of Technology, Masaryk University, Kotlarska 2, CZ-61137 Brno, Czech Republic; (2) Faculty of Science, DCMP, Masaryk University, Kotlarska 2, CZ-61137 Brno, Czech Republic; (3) Institute of Nanotechnology, CNR-NANOTEC, Dept. Chemistry, Via Orabona 4, 70126 Bari, Italy; (4) Center for Surface and Nanoanalytics, Johannes Kepler University in Linz, Altenbergerstrasse 69, 4040 Linz, Austria
Resume : Homoepitaxial SiC layers are promising substrates for a large class of devices, including high frequency and high power switches. We present the results of X-ray and infrared spectroscopy studies of c-axis oriented single-crystalline wafers of 4H SiC with the diameter of 10 and 15 cm. We have used X-ray diffraction mapping of reciprocal space, which provides strain in the samples, and X-ray diffraction topography, providing real space imaging of defects. Lattice vibrations and free carrier response of both doped substrates and undoped epilayers have been quantified using near-normal incidence reflectance and ellipsometric measurements in the infrared spectral range. We have found pronounced polarizability of the free carrier plasma at the longest wavelengths, allowing extrapolations towards low (dc to THz) frequencies. Optical contrast between the substrate and epilayer leads to interference fringes covering the whole spectral range (up to 6000 wavenumbers). The separation of their extrema and the occurrence of beatings are very helpful in assessing the imperfections of epitaxial structures. The strongly polar lattice vibrations couple with free carriers, producing strong modification in the range of LO modes. We have also determined the vibronic contribution to the dispersion of refractive index below the electronic bandgap. Our quantitative results on the free carrier and dielectric screening are relevant for the (opto)electronic operation of 4H SiC.
LED : Mikael Syväjärvi
Authors : Kai Tang, Xiang Ma, Casper van der Eijk, Haiyan Ou2
Affiliations : SINTEF Materials and Chemistry, Trondheim, Norway; Department of Photonics Engineering, Technical University of Denmark, Denmark
Resume : This paper presents our laboratory results of growing a new type of compound semiconductor crystal, i.e. fluorescent silicon carbide (f-SiC), by using liquid solution phase epitaxial (LPE) technology. This new type of f-SiC based white LEDs (WLEDs) represents higher luminous efficiency, better light quality and longer lifespan, compared to the current yellow phosphor based white LEDs. Liquid phase epitaxy technology is able to yield a high crystalline quality in terms of structural perfection owing to the fact that it is a near equilibrium process. In addition, the technological equipment required for LPE is relatively inexpensive. The fundamental backgrounds for LPE growth of Al-doped 4H-SiC are first introduced and elaborated by new thermodynamic and crystal growth models. Based on theoretical analyses, the new designed experimental apparatus is then constructed. The experimental results are presented and discussed. Since operational temperature of LPE growth is much lower than that currently used in physical vapour transport (PVT) process, it is expected to save the energy consumption for SiC crystal growth.
Authors : M. A. Hopkins, S. Thornley, J. Dutson, G. Christmann, M. Benkhaira, C. Ballif, S. Nicolay, J. Niemela, M. Creatore, J. Ellis, D.W.E. Allsopp
Affiliations : M. A. Hopkins; D.W.E. Allsopp are with Dept of Electrical and Electronic Engineering, University of Bath, Bath, BA2 7AY, UK S. Thornley; J. Dutson are with Plasma Quest Ltd, Osbourne Way, Hook, Hampshire, RG27 9UT, UK G. Christmann; M. Benkhaira; C. Ballif; S. Nicolay are with CSEM, Rue Jaquet-Droz 1, 2002 Neuchatel, Switzerland J. Niemela; M. Creatore are with Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands J. Ellis is with Plessey Semiconductors Ltd., Tamerton Road, Roborough, Plymouth, PL6 7BQ, UK
Resume : Low resistance transparent contacts to n-type GaN have the potential to improve the efficiency of high-brightness vertical (i.e. flip-chip) light-emitting diodes (V-LEDs). To date work on forming transparent contacts to V-LEDs in which the emitting surface is the N-polar face of the n-type layer of the device has focussed on using indium tin oxide (ITO),1 however a technology based on earth-abundant elements is preferred for cost reasons. Such Indium-free wide band gap transparent materials typically form Schottky diodes on n-GaN2 and methods for overcoming this limitation are required. In this paper we report a study of the electrical properties of transparent Aluminium or Boron-doped Zinc oxide (AZO) contacts to moderately doped (n ≈ 3 x 1018 cm-3) N-polar n-GaN for vertical LEDs. These contacts are non-ohmic, displaying leaky Schottky barrier behaviour. However, we have developed a surface-modification technology to reliably obtain ohmic contacts between the AZO and N-face n-GaN, giving contact resistances below 2 x 10-5 Ωcm2, which is close to state of the art. This opens the door to creating In-free transparent conducting electrodes for efficient large-area V-LEDs. References 1. D. W. Kim, H. Y. Lee, G. Y. Yeom, Y. J. Sung, J. Appl. Phys. 98, 053102 (2005) 2. T. Han, Y. Shi, H. Wu, C. Liu, Curr. Appl. Phys. 12, 1536-1540 (2012) This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 641864.
Authors : A. Krasnoshchoka, A. Thorseth, C. Dam-Hansen, D. D. Corell, P. M. Petersen, O. B. Jensen
Affiliations : DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, Frederiksborgvej 399, Roskilde, Denmark
Resume : Solid state lighting has made significant progress since early 2000s and has a potential to develop even more over the next decade. Technological advancements have allowed LEDs to be used in variety of lighting applications. Phosphor converted LED has already attracted great interest in terms of high efficiency and light quality, but despite their commercial success, they have one limitation: ”nonthermal droop“ in efficiency with increasing input current density; thus LED chips need to be operated at low current densities for maximum efficiency. An alternative to achieve high-efficient white light sources is to investigate phosphor converted blue laser diodes (PC-LD). Very high power density can be obtained by blue laser diodes. Investigation of saturation effects of phosphors is the key to enable highly efficient and high luminance laser lighting. Here we investigate saturation effects when ceramic phosphors are illuminated by high intensity blue laser light with incident intensities up to 5.8 MW/m.^2. A calibrated integrating sphere setup is used to investigate the spectrum and luminous efficiency of the PC-LD. We find a threshold saturation level where excess incident blue light is not converted into white light. Changes to the spectral content proves to be indicative of saturation in the phosphor. This will be important for future implementation of lighting based on PC-LD in order to simultaneously attain high luminance, high efficiency and good color rendering.
Authors : Tim Senden, Relinde van Dijk-Moes, Andries Meijerink.
Affiliations : Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science, Utrecht University, P.O. Box 80000, 3508 TA Utrecht, The Netherlands
Resume : Solid-state white light emitting diodes (w-LEDs) are attractive alternative light sources for replacing incandescent lamps and (compact) fluorescent tubes due to their increased energy efficiency and long operation life time. Typical high efficacy w-LED lamps are based upon phosphor downconversion of blue InGaN LEDs by Y3Al5O12:Ce3+ (YAG:Ce)-based yellow phosphors. However, an issue for the home lighting market is that the combination of the yellow YAG:Ce emission and blue LED radiation gives ``cool” white light a low color rendering index (CRI < 80). Mn4+-doped fluoride phosphors like e.g. K2SiF6:Mn4+ show bright red luminescence under excitation with blue light which makes them promising to improve the color rendering and energy efficiency of warm white LEDs (w-LEDs). For use of these phosphors in w-LEDs it is important that the red Mn4+ luminescence is not strongly quenched by concentration quenching or thermal quenching. The thermal quenching of Mn4+-doped fluorides has been investigated but it is not understood which non-radiative relaxation process quenches the luminescence. Furthermore, it is not known how the quenching temperature depends on the Mn4+ dopant concentration. Moreover, studies of concentration quenching for Mn4+ ions in fluorides are very limited. In this work we systematically investigate thermal quenching and concentration quenching for Mn4+-activated K2TiF6 by measuring photoluminescence spectra and decay curves in the temperature range of 4 to 600 K for K2TiF6:Mn4+ phosphors with Mn4+ concentrations ranging from 0.01 to 15.7 mol%. It is observed that the luminescence intensity of the K2TiF6:Mn4+ phosphors is quenched between 400 and 500 K for all Mn4+ dopant concentrations. The thermal quenching is explained by thermally assisted crossing between the 4A2 ground state and the 4T2 or charge-transfer excited state. With increasing Mn4+ concentration the decay time of the Mn4+ 2E state does not decrease significantly, which indicates that concentration quenching due to long-distance energy migration is limited for Mn4+ ions in fluorides. This is important for application in w-LEDs as high Mn4+ doping concentrations are required for sufficient absorption of the blue LED light in the parity-forbidden d-d transitions.
SiC : Peter Wellmann
Authors : Didier Chaussende, Yun-Ji Shin, Kanaparin Ariyawong, Jean-Marc Dedulle, Eirini Sarigiannidou, Odette Chaix-Pluchery, Thierry Ouisse
Affiliations : CNRS, Univ. Grenoble Alpes, LMGP, F-38000 Grenoble, France
Resume : Energy challenges are dramatically boosting the development of wide band gap semiconductors, such as silicon carbide (SiC). Despite tremendous efforts, homoepitaxial growth of 4H- or 6H-SiC epilayers on on-axis (0001) surfaces by the standard chemical vapour deposition process still faces the difficult problem of two-dimensional nucleation, giving rise to polytype inclusions. For such specific need, it is interesting to reconsider the old liquid phase epitaxy (LPE) approach. The most recent results on the liquid phase growth of SiC will be exposed, with a special focus on structural quality and doping. The layer properties will be discussed, regarding for instance the emerging field of fluorescent SiC.
Authors : P. Schuh, M. Schöler, G. Litrico, F. La Via, M. Mauceri, P. J. Wellmann
Affiliations : Crystal Growth Lab, Materials Department 6 (i-meet), FAU Erlangen-Nuremberg, Martensstr. 7, D-91058 Erlangen, Germany; Crystal Growth Lab, Materials Department 6 (i-meet), FAU Erlangen-Nuremberg, Martensstr. 7, D-91058 Erlangen, Germany; CNR-IMM, sezione di Catania, Stradale Primosole 50, I-95121, Italy; CNR-IMM, sezione di Catania, Stradale Primosole 50, I-95121, Italy; E.T.C. Epitaxial Technology Center, Sedicesima Strada, I-95121 Catania, Italy;Crystal Growth Lab, Materials Department 6 (i-meet), FAU Erlangen-Nuremberg, Martensstr. 7, D-91058 Erlangen, Germany
Resume : The cubic polytype of SiC shows technological challenges for the bulk-growth such as a high supersaturation, a silicon rich gas phase and a high vertical temperature gradient. However, a significant step for electronic devices like MOSFETs and intermediate band solar cells can be predicted for high quality material due to the high electron mobility and the wide bandgap. We have developed a transfer method for high quality 3C-SiC-on-Si seeding layers (grown by CVD) to SiC carriers to use in sublimation epitaxy (SE). By variation of growth parameters like temperature and growth time we conducted a series of experiments growing approximately 150 µm thick layers of 3C-SiC. Later on we characterized these layers using KOH etching an optical microscopy to evaluate the morphology of the surface and the stacking fault density. In our previous work we already described defects on the surface in the shape of four-sided pyramids featuring the (111) planes. The origin of these defects can be assigned to the nucleation step during the initial growth of 3C-SiC-on-Si in the CVD process. Using our transfer process and the subsequent SE growth we can show that the amount of pyramids on the surface remains the same or may even decrease by variation of the growth rate. Furthermore, by etching the (100) surface of our samples using KOH, we can observe a decrease in the density of stacking faults with increasing growth rate.
Authors : L. F. Flores Escalante1, K. Y. Tucto Salinas1, J. A. Guerra Torres1, 2, A. Töfflinger3, R. Weingärtner1
Affiliations : 1Departamento de Ciencias, Sección Física, Pontificia Universidad Católica del Perú, Av. Universitaria 1801, Lima 32, Perú; 2Materials Science 6, Institute of Materials for Electronics and Energy Technology (I-MEET), Friedrich-Alexander-Universität Erlangen–Nürnberg, Martensstrasse 7, 91058 Erlangen, Germany; 3Chair Materials for Electronics, Institute of Materials Engineering and Institute of Micro and Nanotechnologies MacroNano®, TU Ilmenau, Gustav-Kirchhoff-Str. 5, 98693 Ilmenau, Germany.
Resume : This work is focused on the luminescence study of Yb–Tb co-doped wide bandgap semiconductor a-SiC. The annealing and rare earth concentrations induced o reduced the activation of the Tb3 and Yb3 ions. The luminescence spectra is triggered by an energy transfer between Yb3 and Tb3 .The energy transfer process is studied by changing these conditions, i.e. applying different annealing processes to the samples Co-doped thin film were deposited by radio frequency magnetron sputtering on crystalline silicon substrates. FTIR spectroscopy allowed the identification of bonds with increasing annealing temperature. The XRD verified the crystallization and phase formation of the host matrix. Finally the efficient conversion or absorption of high energy photon is examined by cathodo- and photoluminescence spectroscopy. Keywords: terbium, ytterbium, silicon carbide, photoluminescence, wide band gap semiconductor
Authors : Yi Wei, Ulrike Künecke, Andres Osvet, Valdas Jokubavicius, Mikael Syväjärvi, Peter Wellmann, Haiyan Ou
Affiliations : Department of Photonis Engineering, Technical University of Denmark; Institute of Materials for Electronics and Energy Technology (I-MEET), Department of Materials Science and Engineering, University of Erlangen-Nuremberg;Institute of Materials for Electronics and Energy Technology (I-MEET), Department of Materials Science and Engineering, University of Erlangen-Nuremberg; Department of Physics, Chemistry and Biology, Linköping University; Department of Physics, Chemistry and Biology, Linköping University; Institute of Materials for Electronics and Energy Technology (I-MEET), Department of Materials Science and Engineering, University of Erlangen-Nuremberg; Department of Photonis Engineering, Technical University of Denmark
Resume : We have presented the low temperature photoluminescence (PL) measurements of three 6H fluorescent Silicon Carbide (f-SiC) samples. The epilayers of the f-SiC samples were nitrogen-boron co-doped and grown by fast sublimation growth process (FSGP) method on the bulk 6H SiC substrates. The doping concentrations of the f-SiC epilayers were determined by secondary ion mass spectroscopy (SIMS) showing strong n-type, strong p-type and slight p-type extrinsic semiconductor doping of each epilayer. The PL intensity of one commercial 6H bulk SiC (TanKeBlue Ltd.) was also measured and applied as the reference. The PL was excited by a diode laser source with wavelength of 405 nm and power of 5 mW. The temperature of the PL measurement was ranged from 25K to 300K when the liquid nitrogen cryostat was used, while lower temperature from 5K was achieved when the cryostat with liquid helium was applied. The anomalous temperature dependences of the PL intensity spectrum of f-SiC samples were found. The PL peak energy?s S-shape dependence on the temperature was observed which was caused by nitrogen induced localization effect. For strong p-type f-SiC, one more PL intensity peak at 5 k was observed at wavelength of 520 nm, where this extra PL peak was the result of basal plane dislocation and free-to-acceptor recombination.
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Optoelectronics : Kai Tang
Authors : Olivia Kettner (a), Sanja Simic (b), Birgit Kunert (a), Robert Schennach (a), Roland Resel (a), Thomas Griesser (c), Bettina Friedel* (a,d)
Affiliations : (a) Institute of Solid State Physics, Graz University of Technology, 8010 Graz, Austria; (b) Institute for Electron Microscopy, Graz University of Technology, 8010 Graz, Austria; (c) Chemistry of Polymeric Materials, Montanuniversität Leoben, 8700 Leoben, Austria; (d) Energy Research Center, Vorarlberg University of Applied Sciences, 6850 Dornbirn, Austria
Resume : Silicon carbide (SiC) is a synthetic non-oxide ceramic, extremely heat- and corrosion stable. As a semiconductor, its high charge mobility or breakdown electric field, and operational pn-junctions up to 600°C, make it desirable for high power and high temperature electronics. Like well-known transparent conducting oxides (TCOs), also SiC comprises a wide band gap, enabling its use in optoelectronics. Despite these advantages, it is rarely used for this purpose on a large scale, due to its costly common production via sublimation single crystal growth or thin film epitaxy. Additionally, the introduction of selected dopants, especially p-type, is challenging. Here, we present an approach to silicon carbide, using an alternative sol-gel processing and carbothermal reduction reaction based approach. This method enables not only the preparation of material in versatile forms, such as spherical particles, porous structures, nanowires or bulk materials, but even enables infiltration and solution deposition techniques, just like common sol-gel techniques for oxides. If required, n- and p- doping of SiC is achieved by addition of suitable compounds at the wet-chemical stage. We will show details on the properties of this sol-gel derived SiC material, such as its morphology and surface termination, defects and impurities and how these depend on the introduced dopant. In terms of applications, we will demonstrate its functionality exemplarily for photovoltaic energy conversion in organic-inorganic hybrid solar cells, where SiC qualifies as inorganic acceptor in combination with a photoactive polymer donor, and for photocatalytic electrochemical carbon dioxide back-conversion into fuel, as an alternative to fossil resources.
Authors : Barkha Tiwari and Shanker Ram
Affiliations : Materials Science Centre, Indian Institute of Technology, Kharagpur, India Contact details: +91-9434611138, firstname.lastname@example.org
Resume : Calcium indate (CaIn2O4) is an important wideband gap (3.9 eV) semiconductor that can be explored for optical doping such as transition metals and/or rare-earths useful to make light-emitters, optical data storage, and other devices. Here, we synthesize Cr4+ doped CaIn2O4–C hybrid nanostructure (1-10 mol% Cr4+) in tuning visible-light emission and dielectric properties. When grafting a C-sp2 surface layer on Cr4+: CaIn2O4 of small crystallites it yields a core-shell structure of tailored dielectric, optical and other properties. A green route using fresh nectar from aloe vera leaves is used to produce this structure from Cr6+, Ca2+ and In3+ salts. The aloe vera nectar embeds the cations in a gel so as it controls an ionic conversion Cr6+ Cr4+ in the ambient air [1,2]. When self-dried at room temperature, the gel was burnt with camphor (a fuel) in air to yield a hybrid phase. Free carbon could be burnt out by annealing the powder at 400C in air. In 1 mol% Cr4+ doped sample (measured at room temperature), a dielectric permittivity εr ~ 97 lasts at low frequencies near 1 Hz, and it decays progressively on raising the frequency in a fairly steady εr ~ 3 above 1 kHz. At 105 to 106 Hz frequency, the ac conductivity picks-up suddenly by nearly three orders of magnitude, e.g., 34.5x10-7 Scm-1. A semi-circle that appears of the Nyquist plots at small 1 mol% Cr4+ doping converts into a linear path intrinsic of an insulating behavior at higher Cr4+ contents. As-prepared Cr4+:CaIn2O4–C exhibits two bands at 265 nm and 360 nm, which are shifted to at 270 and 370 nm when it is annealed at 400-600 ºC for 2 h. These are the ligand-to-metal O2- Cr4+ charge transfer bands. The light-emission is studied in analyzing migration, transfer and recombination processes of light-induced e--h+ pairs. Upon exciting at a 270 nm wavelength from a xenon lamp, two broad emission bands appear at 395 nm and 680 nm as intense blue and red lights. The intensity decreases in both the bands on annealing the sample as a result of a suppressed e--h+ recombination. The results are described in correlation to a hybrid Cr4+:CaIn2O4–C structure.
Authors : Stefan Edinger, Neha Bansal, Martin Bauch, Rachmat Adhi Wibowo, Raad Hamid, Gregor Trimmel, Theodoros Dimopoulos
Affiliations : AIT Austrian Institute of Technology, Center for Energy, Photovoltaic Systems, Vienna, Austria; AIT Austrian Institute of Technology, Center for Low-Emission Transport, Vienna, Austria; Graz University of Technology, Institute for Chemistry and Technology of Materials, Graz, Austria
Resume : The chemical bath deposition has potential as a cost-efficient fabrication technique for transparent electrodes for thin film photovoltaics. In this work we investigate chemical bath-deposited ZnO films, undoped or doped with the group-13 metals Al, Ga and In. The study shows marked differences in dopant incorporation in the films, depending on the dopant type. The addition of dopant salt in the solution modifies the deposition rate, with maximum achieved rate close to 100 nm/min. X-Ray diffraction showed that all films have the (002) texture, whereas the lattice stress suggests substitutional incorporation at Zn sites for specific dopants and concentrations. The average visible transmittance is higher than 80%, while the infrared reflectivity increases with the free carrier density, which is the lowest for undoped ZnO (10^19 cm^-3) and increases up to 1 order of magnitude for doped films. Optical measurements reveal an inverse correlation between carrier density and mobility. Doping enlarges the bandgap and the Urbach energy that is related to the film disorder. The lowest electrical resistivity, measured by four-point probe, is 0.017 Ω∙cm. The stability of the films upon exposure to high doses of UV irradiation is also investigated.
Authors : Benjamin A.D. Williamson(1), John Buckeridge(1), Robert G. Palgrave(3), David O. Scanlon(1,2)
Affiliations : (1) University College London Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, UK ; (2) Diamond Light Source Ltd. Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK ; (3) University College London, Christopher Ingold Building, Department of Chemistry, London WC1H 0AJ, UK
Resume : The paucity of high performance p-type semiconductors has been a stumbling block for the electronics industry for decades, effectively hindering the route to efficient p-n junctions. Through the “chemical modulation of the valence band” (CMVB) pioneered by Hosono et al.,(1) copper based oxides and subsequently copper based chalcogenides have been a focal point for designing efficient p-type semiconductors, particularly transparent semiconductors. Our work extends this concept further into the pnictides with a group of ternary copper phosphides, M(II)CuP (where M(II) = Mg, Ca, Sr and Ba) and explores the relationship between coordination and band dispersion alongside explaining the coordination preference of Cu(I) based materials. Using hybrid density functional theory (DFT) we examine the structural and electronic properties of these four materials where we find hole effective masses matching the industry standard n-type TCOs: In2O3, ZnO and SnO2 paving the way towards the design of high performance p-type materials. (1) Kawazoe, H. et al. P-type electrical conduction in transparent thin films of CuAlO2. Nature 389, 939–942 (1997). (2) Williamson, B. A. D. et al. Engineering Valence Band Dispersion for High Mobility P-Type Semiconductors. Chem. Mater. (2016). doi:10.1021/acs.chemmater.6b03306
Optoelectronics : Satoshi Kamiyama
Authors : Chao Ping Liu, Cheuk Kai Kwok, Chun Yuen Ho, J. A. Zapien, Kin Man Yu
Affiliations : Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Ave., Kowloon, Hong Kong
Resume : Because of the low temperature processing, high carrier mobility, good transparency over a wide spectral range as well as large area uniformity and excellent mechanical flexibility, amorphous transparent conducting oxides (a-TCOs) have attracted increasing attention recently especially in flexible electronics applications. In comparison with other TCOs, CdO has the highest reported mobility of 200-500 cm2/Vs at an electron concentration of 10^20-10^21 cm-3. However, CdO has a relatively low intrinsic bandgap (~2.2 eV), resulting in a compromised transparency window in the UV region. Alloying of CdO with other wide bandgap semiconductor may result in a-TCOs with high mobility and high transparency. In this work, we have synthesized In2O3-CdO alloy thin films at room temperature using radio frequency magnetron sputtering on glass over the entire alloy composition range. Rutherford backscattering and x-ray diffraction show that In1-xCdxO films with 0.1
Authors : V. S. Olsen, B. G. Svensson, A. Kuznetsov, L. Vines
Affiliations : University of Oslo, Physics Department/Center for Materials and Nanotechnology, P.O. Box 1048 Blindern, N-0316 Oslo, Norway
Resume : Bandgap engineering plays an important role in designing novel functionalities in semiconductor materials. ZnO and GaN are applicable for optoelectronic devices and exist in the wurtzite hexagonal structure (WZ) with similar lattice constants. Interestingly, combining the two wide-bandgap semiconductors, both having a band gap of ~3.4 eV, results in a strong band bowing effect where the band gap of a 50% alloy can reach 2.4 eV . In the present work, (ZnO)1-X(GaN)X thin films with X ranging from 0 to about 0.2 are deposited on sapphire substrates using RF magnetron sputtering. X-ray diffraction on the as-deposited samples shows a shift in the (0002) peak for increasing GaN content, while transmission measurements show a shift to longer wavelengths, in accordance with a reduced bandgap and previously reported results. The structural properties remain similar during post-deposition annealing up to 800oC for 1 hour, whilst a steeper on-set in the transmission measurements is observed. Moreover, photoluminescence measurements on as-deposited samples exhibit a broad near band edge luminescence, while post growth annealing at 800oC restores the luminescence properties to those of a ZnO like film. Further, transmission electron microscopy measurements and Rutherford backscattering spectrometry results will be discussed.  Chen et al. J. Phys. Chem. C 114, 1809 (2010).  K. Maeda et.al. J. Phys. Chem. B. 2005, 109, 20504-20510.
Authors : J. Montero, F. A. Martinsen, S. Zh. Karazhanov, E. S. Marstein
Affiliations : Institute for Energy Technology, P.O. Box 40, NO-2027 Kjeller, Norway
Resume : Oxygen-containing yttrium hydride (YH_aO_b) thin films deposited by magnetron sputtering possess wide band gap and high luminous transmittance in the visible spectrum. Studies carried out in our group have shown how the luminous transmittance (Tlum) of the YH_aO_b thin films decreases significantly when illuminated with light of adequate wavelength and intensity. This decrease in the transmittance is reversible, i.e., the films recovered gradually their initial transparency once the illumination was interrupted, and thus YH_aO_b emerged as a new T-type positive photochromic material. Photochromic materials have many applications in smart fenestration, ophthalmic lenses, agricultural films, security markings and many more. The objective of this work is to explore, from an optical perspective and aiming to a technological application, the possibilities that this photochromic material can provide in terms of transparency in the clear state and modulation of the optical transmittance. On this basis, the optical properties of a set of YH_aO_b thin films, deposited by magnetron sputtering under different conditions, has been studied by spectrophotometry and ellipsometry before and after being illuminated during 1 hour at 1 Sun. Our results show how YH_aO_b thin films with excellent transparency in the visible spectrum, Tlum above 80 %, can reduce reversibly their initial luminous transmittance by more than 30 %. In addition, a theoretical model able to reproduce quantitatively the optical properties of the films, both in their clear and photodarkened state, is presented.
Authors : Hoang-Long Le Tran, Eirini Sarigiannidou , Odette Chaix-Pluchery, Isabelle Gélard, Thierry Ouisse and Didier Chaussende
Affiliations : Univ. Grenoble Alpes, CNRS, LMGP, F38000 Grenoble, France
Resume : Al4SiC4 is a refractory ceramics with a band gap of about 2.5eV, making it an interesting semiconductor material for various applications in the field of energy. The synthesis of Al4SiC4 single crystals has so far not been investigated. In this study, the sublimation growth method is explored as a potential route for getting single crystals. Combining a thermodynamic analysis with an extensive experimental approach, vaporization and condensation phenomena in the Al4C3 - SiC system are described. Initial composition, temperature and temperature gradient are investigated and optimized regarding the crystallization of Al4SiC4.
Authors : Samvit G. Menon, Suresh D. Kulkarni, K. S. Choudhari, S. A. Shivashankar, and Santhosh C.
Affiliations : Samvit G. Menon; Suresh D. Kulkarni; K. S. Choudhari; and Santhosh C - Department of Atomic and Molecular Physics, Manipal University, Manipal, Karnataka, India-576104 S. A. Shivashankar - Centre for Nano Science and Engineering, Indian Institute of Science, Bengaluru, Karnataka, India -560012
Resume : A rapid, 10 min microwave-assisted synthesis of ZnAl2O4 spinel using metalorganic precursors is reported. Nanocrystalline ZnAl2O4 of high phase purity was formed in situ at temperatures as low as 185 °C. The effect of annealing nanoparticles at temperatures in the range 500- 1200 °C on their structural and optical properties was investigated. Crystallite sizes, determined from the XRD patterns, varied from 5 nm in the as-prepared form, to 31 nm when annealed at 1200 °C. The crystallites did not display any definite shape; polyhedral crystallites with well-defined grain boundaries can be seen in the HR-TEM image of annealed samples. Diffuse reflectance spectroscopy (DRS) gives insight into the structural development of the spinel, whereas photoluminescence spectroscopy shows that antisite defects - in the form of zinc interstitials caused by cationic redistribution in a partially inverted spinel and in the form of oxygen and zinc vacancies - governs the different emission bands of the spinel. The investigation of optical properties shows that inhomogeneity in cationic distribution, caused by the rapid synthesis method, is prevalent even after annealing at 1200 °C. Microwave-assisted synthesis opens new opportunities for the rapid synthesis of doped ZnAl2O4 phosphors suitable for display and sensing applications.
LED : Haiyan Ou
Authors : Alaa eldin GIBA1,2, Philippe PIGEAT1, Stéphanie BRUYERE1, Hervé RINNERT1, Flavio SOLDERA2, Frank MÜCKLICH2, Raul GAGO-FERNANDEZ3, David HORWAT1
Affiliations : 1Institut Jean Lamour – UMR CNRS 7198– Université de Lorraine, Nancy, France; 2Department Materials Science and Engineering, Saarland University, D-66123 Saarbrücken, Germany; 3Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, E-28049 Madrid, Spain.
Resume : Rare earth-doped III-nitrides such as GaN and AlN, attract great attention in lightening and optoelectronic applications. Particularly, AlN with large optical bandgap (6.2 eV) can offer an opportunity to cover wide range of light spectrum from UV to IR regions. In addition, AlN with high thermal conductivity (300 W/mK) is a very suitable material for high power working optoelectronic devices. Exploiting the large bandgap and the thermal conductivity features of AlN lead to open the door for generating blue emission with low thermal quenching effect even at high power operation. These are very interesting prerequisites for establishing stable white light emitting diodes (w-LED). Seeking for realization the blue emission from AlN, cerium-doped aluminum nitride (Ce-AlN) thin films were prepared at room temperature using radio frequency (RF) reactive sputtering. X-ray diffraction and high resolution transmission electron microscopy (HRTEM) revealed a well crystalline textured microstructure with single <002> out-of-plane orientation. Strong blue emission from the prepared samples was detected when excited by 325 nm laser. Electron energy loss spectroscopy (EELS) has been used to reveal the dominant oxidation state of Ce atoms, which undergoes a change from of Ce(IV) to Ce(III) ions after annealing. The chemical composition was analyzed by simulation of Rutherford backscattering spectrometry (RBS) and compared to HRTEM images. A clear correlation between microstructure, composition and sample photoluminescence (PL) was established. It was found that surface oxidation during post-deposition annealing plays an important role in the PL response of the samples. The role of oxygen in the excitation mechanism was explained from the photoluminescence excitation measurements. We believe that the strong blue emission in this new (oxy)-nitride material holds great potentials for solid state lighting applications due to its thermal and chemical stability as well as the luminescence efficiency. Moreover, the comprehensive approach conducted within this study could serve as a guideline for better understanding and the design of the luminescence behavior in rare earth-doped (oxy)-nitride thin films.
Authors : A. Lesage, A. Capretti, T. Inaba, T. Kojima, B. Mitchell, A. Koizumi, T. Gregorkiewicz and Y. Fujiwara
Affiliations : Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands; Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Osaka, Japan
Resume : Eu/O co-doped GaN is a promising material for light emitting diodes (LEDs) in the red. However a further increase of the emission intensity is required for commercial application. The emission intensity of the currently available state-of-the-art materials is limited due the relatively long radiative lifetime (~200 μs) of the Eu ions as well as the low optical activity of Eu ions (typically 1%-10% ). In this work, we demonstrate that it is possible to enhance emission intensity by use of a carefully designed nanostructuring of Eu,O-codoped GaN layers grown by organometallic vapor phase epitaxy (OMVPE) – by creating a metamaterial. By using this approach we demonstrate up to two fold increase of emission intensity for the nanostructured material, where up to 87% of the total number of Eu3+ ions have been removed. We explore the different mechanisms which could account for this enhancement, and conclude that it is most probably due to the higher effective excitation cross-section of Eu.  Scientific Reports 4, 5235 (2014)
Authors : P. Louro, M. A. Vieira, M. Vieira
Affiliations : Electronics Telecommunication and Computer Dept. ISEL, R. Conselheiro Emídio Navarro, 1949-014 Lisboa, Portugal Tel: 351 21 8317290, Fax: 351 21 8317114, email@example.com ; CTS-UNINOVA, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal. DEE-FCT-UNL, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal
Resume : White LEDs are currently an energy saving lighting solution that constitutes an integrated solution for environmental lighting and communication technologies which constitutes the technology Visible Light communication (VLC). In this paper we propose the use of RGB white LEDs in an integrated lighting/VLC system for indoors navigation. The constituent red, green and blue chips are modulated at specific frequencies and bit rates. The spatial distribution of the signals is dependent on the geometrical configuration of the LEDs and enables a correspondence among cardinal directions and intensity/wavelength/frequency of the optical signals. The detection is done with a photodetector based on two stacked pin heterostructures of a-Si:H and a-SiC:H that works as an optical filter in the visible range. Optoelectronic characterization of the device is presented and includes spectral response, transmittance and I-V characteristics. Results show that under front bias the photocurrent is amplified in the range of longer wavelengths and quenched in the shorter wavelengths. The use of a back optical bias produces the opposite effect. This feature is used for the identification of the optical excitation. Fourier transform is used for signal frequency identification. Analysis of the photocurrent signal dependence on the LED intensity is done to infer the accurate position of the photodetector. The viability of the system was demonstrated through the implementation of an automatic algorithm.
Authors : A.V.Gradoboev [1,2], A.V. Simonova 
Affiliations :  National Research Tomsk Polytechnic University, Tomsk, Russia;  Joint-Stock Company “Research Institute of Semiconductor Devices”, Tomsk, Russia
Resume : Light-emitting diodes (LEDs) are broadly used in microelectronic devices that operate in space conditions and at nuclear power plants. It is necessary to compare combined and complex effects of ionizing radiation and long-term operation factors both simultaneous and separately for solving problem of these influences on criterion parameters. The purpose of this research is comparison of mechanisms of emissive power change of IR-LEDs based upon AlGaAs double heterostructures under influence of ionizing radiation and long-term operation. Irradiation was implemented using 60Co gamma-quanta in passive power mode. Long-term operation conditions were realized by step-by-step tests. Operating current was increased from step to step with constant ambient temperature (+65 C). Duration of each step was 24 hours. We have established that change of emissive power of LEDs in both cases can be described by three stages. On first stage the emissive power of LEDs decreases due to reconstruction of initial defect structure of LED crystal. On second stage the emissive power of LEDs goes down due to introduction of new defects. Second stage is limited to transition of LED to low injection mode and further catastrophic failure (third stage). Correlations between irradiation dose and step number have been determined for first and second stage of decrease of emissive power of LEDs. The problem of evaluation of reliability indexes of LEDs based on results of their radiation resistance has been discussed.
Authors : Mingue Shin, Joonyun Kim, Byungha Shin*
Affiliations : Department of Materials Science and Engineering, KAIST
Resume : Organic metal halide perovskites (CH3NH3PbX3) have been widely studied for various applications such as light-emitting diodes (LEDs), photovoltaics, lasers or sensors. In particular, organic metal halide perovskites have emerged as a next generation light emitter in LED application because of their outstanding color purity (full width at half maximum of electroluminescence spectra as narrow as 20 nm), easily tunable bandgap through adjustment of the halide element ratio, and low materials cost. However, methylammonium lead bromides (CH3NH3PbBr3) which are suitable for green light emission, have a low exciton binding energy and have a tendency to form cubic shaped crystals, making it difficult to obtain a uniform film. Therefore, the device performance of perovskite LEDs has not yet approached that of OLEDs or QLEDs. Here, we studied the effect of varying molar ratio of the perovskite precursors (MABr and PbBr2) on the properties of synthesized MAPbBr3 thin films as well as on LED device performance. The molar ratio (MABr/PbBr2) was adjusted from 1 (stoichiometry) to 2 (excess MABr) in precursor solution. Structural characterization revealed that the excess MABr condition led to the formation of a new crystalline phase, which appeared to be one of methylammonium compounds, within the MAPbBr3 films. The excess MABr sample also exhibited highest PL intensity, which suggested less occurrence of non-radiative recombination compared to other molar ratios. Based on the PL, the excess MABr was expected to produce the best LED performance, however, it was when MABr/PbBr2 is 1.05 found that led to the best performance. We explain these results by other electronic properties such as Urbach tail energy that we found relevant to the operation of LEDs. With further optimization of hole injection layer, we achieved highly efficient green perovskite LEDs with luminance = 1032.1 cd/m2, current efficiency = 0.905 cd/A and external quantum efficiency (EQE) = 0.198%. Details of characterization results with varying molar ratios and optimization of LED device structures will be presented.
Poster session : The organizers
Authors : 1Soonho Park, 1Jongho Ryu, 2Taewook Kang, 3Sunghoon Lee, 4Heelack Choi, 1Jongsu Kim
Affiliations : 1Department of display engnieering, Pukyoung National University, Busan, 608-737, South Korea 2Interdisciplinary Program of LED and Solid State Lighting Engineering, Pukyong National University, Busan, 608-739, South Korea 3P-Project Team, Hyosung Corporation, Gyeonggi-do, 431-080, South Korea 43Department of Materials Science Engineering, Pukyong National University, Busan, 608-739, South Korea
Resume : High-power white-light-emitting phosphor plate excited by blue lase diode is presented. The yellow Y3Al5O12:Ce phosphor films on various substrates were formed through a thermal diffusion of phosphor compositions into the substrates. For the best blue-to-yellow conversion efficiency, the thickness of phosphor film was optimized with varying the diffusion parameters; temperature, time, pressure. The corelation between surface morphology and optical powder was expected by a light simulation by Lighttools. For the practical applications such as car headlamp and beam projector, the excitation power and temperature dependences was analyzed together with Raman measurement for photon-phonon coupling effect.
Authors : Mr. SUMIT KUMAR
Affiliations : Dr. B R Ambedkar National Institute of Technology Jalandhar, India
Resume : Purpose: As a number of buildings are increasing day by day due to the opening of new industries, colleges, hostels, hospitals, etc. Therefore there is continuously increase in energy consumption by these buildings and this scarcity of electricity is compensated by limiting the electricity supply to our villages for irrigation and other usages.As also people who want lands for plotting purpose are looking towards agricultural lands and using solar panels for electricity purposes. Mostly the agricultural lands experience the destruction due to the rise in temperature of the particular region where solar panels are installed. The purpose of the research is to use green energy(solar energy) in the way that it doesn't harm the mother nature. And this can be done by directly transferring the incoming photons to the targeted area using a special class of fiber optics. Methods: 1. Effects and properties of agriculture land before and after installation of solar panels. 2. Testing the heat radiation of Solar panels in static mode (stationary points are installed). 3. Testing for the orientation of fiber optics to catch the maximum of the photons. 4. Testing the suitable way to eliminate heat after illumination by using fiber optics. Results: There is some heat evolved when using the static or dynamic model of solar panels to convert light energy into electricity while no heat is evolved when photons are transferred directly to the targeted area using a special class of fiber optics. Conclusion: The static and dynamic mode solar panels dissipate heat while converting photon's energy into electric energy whereas while transporting the photons directly to the targeted area does not dissipate or evolve any heat energy. Thus global warming can be reduced by up to small extent by decreasing the consumption of solar panels for such uses. References: 1. Jeff Hecht, City of light: the story of fiber optics, OXFORD UNIVERSITY PRESS, 14-24, 1999. 2. K. C. Kao, Physical aspects, Dielectric-fibre surface waveguides for optical frequencies, Vol. 113, No. 7, 1156-1159, 1966. 3. Dr. N.Chandrashekar, Sun Tracking Device, Patent.No.251549, July-2012 4. Tarujyoti Buragohain, Impact of Solar Energy in Rural Development in India, IJESD, Vol. 3, Pg:334-338, 2012
Authors : Mehmet Isik, Nizami Hasanli
Affiliations : Department of Electrical and Electronics Engineering, Atilim University, Ankara, Turkey (Mehmet Isik); Physics Department, Middle East Technical University, Ankara, Turkey (Nizami Hasanli)
Resume : GaS(x)Se(1-x) mixed crystals are formed from the GaSe and GaS semiconducting materials with x ranging from 0 to 1. By varying the composition its energy gap covers a wide range of the visible spectrum. Taking into consideration the technological applications of GaSe and GaS, GaS(x)Se(1-x) crystals can be important candidate in the usage areas of constituent compounds. Ellipsometry is a powerful and non-destructive optical characterization technique based on the change of the amplitude and phase of the polarized light after reflection from the sample. Analyses of the ellipsometric data are used to get detailed information about the optical constants and electronic band structure of samples. Spectroscopic ellipsometry measurements were performed on GaS(x)Se(1-x) mixed crystals (0 ≤ x ≤ 1) in the 1.2-6.2 eV range. Spectral dependence of optical parameters; real and imaginary components of pseudodielectric function, pseudorefractive index and pseudoextinction coefficient were reported. Critical point (CP) analyses on second-energy derivative spectra of the pseudodielectric function were accomplished to find the interband transition energies. The revealed energy values were associated with each other taking into account the fact that band gap energy of mixed crystals rises with increase of sulfur composition. Peaks in the spectra of studied optical parameters and CP energy values were observed to be shifted to higher energy values as sulfur concentration is increased in the mixed crystals.
Authors : Nizami Hasanli, Mehmet Isik, Ahmet Ogan
Affiliations : Physics Department, Middle East Technical University, Ankara, Turkey (Nizami Hasanli; Ahmet Ogan); Department of Electrical and Electronics Engineering, Atilim University, Ankara, Turkey (Mehmet Isik)
Resume : GaSe and GaS are attractive materials in technological applications such as field-effect transistors, photovoltaic, optoelectronic, energy conversion and storage, topological insulators, nonlinear optical devices and photodetectors. Moreover, investigations on GaSe/GaS revealed the potential usage of the structure as ultrathin layer transistors. GaSe and GaS crystals form GaS(x)Se(1-x) mixed crystals with x ranging from 0 to 1. Taking into consideration the technological applications of GaSe and GaS, GaSxSe1-x mixed crystals have potential to be used in the fabrication of long-pass filter, light emitting devices and optical detecting systems. Transmission and reflection measurements on GaS(x)Se(1-x) mixed crystals were performed in the 400-1000 nm spectral range. Band gap energies of the studied crystals were obtained using derivative spectrophotometry analyses. Compositional dependence of band gap energy revealed that as sulfur composition is increased in the mixed crystals, band gap energy increases quadratically from 1.99 eV (GaSe) to 2.55 eV (GaS). Spectral dependencies of refractive indices of the mixed crystals were plotted using the reflectance spectra. It was observed that refractive index decreases nearly in a linear behavior with increasing band gap energy for GaS(x)Se(1-x) crystals. Atomic compositions of the studied crystals obtained from the energy dispersive spectroscopy measurements are well-matched with composition x increasing from 0 to 1 by intervals of 0.25.
Authors : A.V.Gradoboev [1,2], A.V. Simonova , K.N. Orlova 
Affiliations :  National Research Tomsk Polytechnic University, Tomsk, Russia;  Joint-Stock Company ?Research Institute of Semiconductor Devices?, Tomsk, Russia
Resume : Light-emitting diodes (LEDs) may be operated under conditions of various ionizing radiation. In these operating conditions reliability of LEDs is determined by combined influence of ionizing radiation and long-term operation factors. The purpose of this work is research of the influence of preliminary irradiation by gamma-quanta and neutrons on the reliability of IR-LEDs. Matter of the research is IR-LEDs based upon AlGaAs double heterostructures. Preliminary irradiation was implemented using 60Co gamma-quanta and fast neutrons without electric supply. Then long-term operation conditions were realized by step-by-step increase of operating current with constant ambient temperature (+65 C). Duration of each step was 24 hours. Two characteristic radiation levels were chosen for preliminary irradiation by both gamma-quanta and neutrons. The first irradiation level corresponded to first stage of emissive power decrease of the LEDs under the influence of ionizing radiation (the radiation-stimulated reconstruction of the initial defect structure of the LED crystal). The second irradiation level corresponded to second stage of emissive power drop of the LEDs (the introduction of radiation defects). The preliminary irradiation by gamma-quanta has increased useful lifetime of the LEDs, which allows to use gamma-quanta in the manufacturing technology of LEDs for rise their reliability. Preliminary irradiation by fast neutrons has led to reduce threshold of catastrophic failures appearance due to accelerate degradation of ohmic contacts. Under specific conditions the irradiation by fast neutrons may be recommended for manufacture of LEDs with improved reliability. Probable causes of observable results are discussed.
Authors : Arijit Sarkar, Ajit K. Katiyar, S. Mukherjee and Samit K. Ray
Affiliations : Advanced Technology Development Center, Indian Institute of Technology, Kharagpur-721302, India; Department of Physics, Indian Institute of Technology, Kharagpur-721302, India; Advanced Technology Development Center, Indian Institute of Technology, Kharagpur-721302, India; Department of Physics, Indian Institute of Technology, Kharagpur-721302, India
Resume : Silicon based flexible UV-visible photodetectors can play an important role in optoelectronic applications due to its compatibility with existing CMOS technology and its adaptability where flexibility and agility of the device is required. Here we report the development of a n-ZnO/p-Si membrane heterojunction based flexible photodetector sensitive to both UV and visible photons. The 3 µm thick Si membrane was fabricated by the alkaline etching method followed by deposition of ZnO thin film (120 nm) by RF sputtering. At zero applied bias, a peak responsivity of 0.20 AW-1 with detectivity of 4.8 × 1011 cm Hz1/2 W-1 has been obtained. The flexibility of the Si membrane as substrate has motivated us to utilize the piezo-phototronic effect in ZnO to improve the performance of the fabricated device. Strain induced piezo-potential developed in piezoelectric ZnO thin film has been utilized to modulate the transport property of the photo generated carriers thereby positively affecting the device performance. With the gradual increase in the external tensile strain the photocurrent has increased from 5.5 mA to 6.7 mA. The accompanying simulation analysis reveals the piezopotential distribution developed in the ZnO film on application of stress to the heterojunction.
Authors : Hyun-Woo Park1, Kwun-Bum Chung1*, Dukhyun Choi2, Jang-Yeon Kwon3
Affiliations : 1Division of Physics and Semiconductor Science, Dongguk University, Seoul, 100-715, Korea ; 2Department of Mechanical Engineering, School of Engineering, Kyung Hee University, Yongin, 446-701, Republic of Korea ; 3Yonsei Institute of Convergence Technology, Yonsei University, Incheon, 406-840, Korea
Resume : The device performance and stability of staggered bottom gate structure tungsten-indium-zinc oxide thin film transistors (WIZO-TFTs) were fabricated by a radio frequency (RF) co-sputtering system using the WIZO and indium-tin oxide (ITO) source/drain (S/D) electrode materials on a same WIZO active channel layer. The electrical device characteristics of the WIZO film as the S/D electrode and the active channel layer, were adjusted by the oxygen partial pressure in the deposition process, respectively. The improvement of the device performance and stability with WIZO and ITO S/D electrodes, and their correlations between the device performance and the physical properties at the interface region were investigated in terms of contact resistance, interface roughness, interfacial trap density, interfacial energy level alignments. The WIZO-TFT with WIZO electrodes exhibited the lower contact resistance, lower interfacial trap density, and more flat interface roughness than the WIZO-TFT with ITO electrodes. Furthermore, the electron barrier of the WIZO-TFT with WIZO electrodes is 0.09 eV, which is lower than the value of 0.21 eV was obtained for the WIZO-TFT with ITO electrodes. This reduced electron barrier could be attributed to the improvement of device performance and stability, because of the electron transport.
Authors : M. M. Afandi, T.W. Kang, W.T. Jang, S.H. Park, J.S. Kim
Affiliations : Department of Display Engineering, Pukyong National University, 608-737, Republic of Korea; Interdisciplinary of LED and Solid State Engineering, Pukyong National University, 608-737, Republic of Korea; Department of Display Engineering, Pukyong National University, 608-737, Republic of Korea; Department of Display Engineering, Pukyong National University, 608-737, Republic of Korea; Department of Display Engineering, Pukyong National University, 608-737, Republic of Korea
Resume : Light and sound-emitting electroluminescent (EL) device has been achieved by constructing phosphor layer on piezoelectric dielectric layer. The EL device consists of screen-printed ZnS:Cu,Al phosphor on high piezoelectric material Pb(Zr,Ti)O3 (PZT). The PZT dielectric layer showed the high dielectric effect reducing threshold voltage up to 10 V, and its high strain effect produced a high sound level up to 60 dB. As the increasing of voltage (10 V - 200 V), the light intensity increased without a spectral change and the sound level increased without tone frequency change. However, as the increasing of frequency (10 Hz – 1 MHz), the light intensity increased with a blueshift, and it sound level increased with a change of tone frequency. The tone frequency was same with the frequency of applied voltage, as a result, all diatonic tones was achieved by adjusting the applied frequency into diatonic frequencies. Furthermore, the temperature dependence of this device showed that the optical and acoustical functions are so different. It is the reason why the former results from the phosphor, but the latter comes from the PZT.
Authors : C. S Lee*,1, W. C. Hsu2, H. Y. Liu1, B. J. Chiang1, Y. C. Chen1, S. T. Yang1, C. G. Lin1, X. C. Yao1, J. Y. Lin1, Y. T. Shen1, and Y. C. Lin1
Affiliations : 1: Department of Electronic Engineering, Feng Chia University, 100, Wenhwa Road, Taichung, Taiwan 40724, R.O.C. 2: Institute of Microelectronics, Department of Electrical Engineering, National Cheng-Kung University, 1, University Road, Tainan, Taiwan 70101, R.O.C.
Resume : Ti0.5Al0.5O-dielectric Al0.26Ga0.74N/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) grown on a Si substrate are investigated. The Ti0.5Al0.5O gate dielectric was grwon by using a cost-effective non-vacuum ultrasonic spray pyrolysis deposition (USPD) technique. The effective oxide thickness (EOT) was determined to be 2.68 nm with high dielectric constant k = 9.01. Improved interfacial quality is studied by comparisons of Hooge coefficient (αH), low-frequency noise spectra (1/f), pulse I-V characteristics. As compared to a reference Schottky-gate HEMT, superior improvements have been achieved for the present MOS-HEMT design, including 23% in maximum drain-source current density (IDS, max), 31% in gate-voltage swing (GVS) linearity, 3-order increases in on/off current ratio (Ion/Ioff), 46.3% in two-terminal off-state gate-drain breakdown voltage (BVGD), 65% in three-terminal drain-source breakdown voltage (BVDS), 28% in unity-gain cut-off frequency (fT), and 46% in maximum oscillation frequency (fmax). Enhanced power performances and thermal stability at 300-450 K are also obtained. The present design is advantageous to high-gain and high-power circuit applications. KEYWORDS: MOS-HEMT, Ti0.5Al0.5O, ultrasonic spray pyrolysis deposition.
Authors : T. Sameshima, Y. Ogawa, M. Hasumi
Affiliations : Tokyo University of Agriculture and Technology
Resume : We discuss optical reflection loss at intermediate adhesive layer for mechanically stacked multi junction solar cells. Good electrical connection between top and bottom semiconductor substrates has been achieved with a connecting resistivity lower than 0.5 ohmcm2 by dispersing 0.02-mm-ITO particles in an epoxy adhesive layer. We propose conductive and transparent IGZO layers as optical anti-reflection layer formed between the semiconductor substrate and intermediate adhesive to reduce optical reflection loss. 130-nm-thick 0.01-ohmcm IGZO layers were formed on surfaces of GaAs and Si substrates by plasma sputtering. The IGZO surfaces of two substrates were pasted with epoxy adhesive jell dispersed with 3.8-wt%-ITO particles and stacked to make a structure of GaAs/IGZO/adhesive/IGZO/Si. The optical reflectivity was 0.33 for wavelength between 902 and 1020 nm, where the top GaAs is transparent and bottom Si is opaque. This value was close to the optical reflectivity at the top GaAs surface. A low optical reflection loss was estimated as 0.06 because of anti-reflection condition of IGZO layers. Similar low optical reflectivity was observed with different incident angles of light. The optical reflection loss was 0.04 for an incident angle of 20 degrees. In contrast, the optical reflectivity was high of 0.41 for GaAs/adhesive/Si with no IGZO. This paper will also report optical reflection loss for different sample of GaP/IGZO/adhesive/IGZO/Si.
Authors : M. A. Vieira, M. Vieira, P. Louro, P. Vieira
Affiliations : Electronics Telecommunication and Computer Dept. ISEL, R. Conselheiro Emídio Navarro, 1949-014 Lisboa, Portugal Tel: 351218317290, Fax: 351218317114, mv@ isel.ipl.pt ; CTS-UNINOVA, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal. DEE-FCT-UNL, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal Instituto de Telecomunicações, Instituto Superior Técnico, 1049-001, Lisboa, Portugal
Resume : We propose the use of Visible Light Communication (VLC) for vehicle safety applications, creating a smart vehicle lighting system that combines the functions of illumination, signaling, communications, and positioning. The proposed coding is based on SiC technology. The system is a self-positioning system. Trichromatic Red-Green-Blue LEDs (RGB-LED) are used together for illumination proposes and individually, each chip, to transmit the channel location and data information. The chips of the RGB-LEDs can be switched on and off individually, in a desired bit sequence to transmit the information. The receivers consist of two stacked amorphous cells [p(SiC:H)/i(SiC:H)/n(SiC:H)/p(SiC:H)/i(Si:H)/n(Si:H)] sandwich between conductive transparent contacts. The receiver and the transmitters are characterized through spectral response, I-V characteristics and transmittance measurements under different optical bias. The spectral sensitivity of the receiver as a function of the distance from the transmitters is analysed. An optoelectronic model gives insight into the physics of the system. The receivers join the simultaneous demultiplexing operation with the photodetection and self-amplification. The information and the code position of each LED are transmitted simultaneously through the RGB pulsed transmitted channels. A violet LED is used for error control. Free space is the transmission medium. An on-off code is used to transmit data. An algorithm to decode the information is established.
Authors : Ravi Raninga, Robert L. Z. Hoye, Judith Driscoll
Affiliations : University of Cambridge, University of Cambridge, University of Cambridge
Resume : ZnO has received much renewed interest as a wide band gap semiconductor for its variety of applications. For certain applications, such as thin film transistors, it is important to have highly crystalline ZnO with few defects, as a high defect concentration introduces too many charge carriers and can contribute to source-drain leakage. In this paper, we present a new roll-to-roll process, namely UV-Assisted Atmospheric Pressure Spatial Atomic Layer Deposition, for synthesizing high quality, crystalline ZnO. Using X-ray diffraction techniques, we show that the UV-activation of diethylzinc allows us to deposit c-axis oriented ZnO at temperatures as low as 50 C with significantly improved crystallinity. This temperature is significant as it is below the glass transition temperature of polyethylene terephthalate (PET), a popular substrate in the field of flexible electronics. Our new process allows us to overcome the tendency of ZnO to be amorphous when grown below 100 C. We also present the effect of growth under UV-illumination at different wavelengths on the defect states in ZnO with the use of X-ray photoemission spectroscopy, photothermal deflection spectroscopy and photoluminescence.
Authors : Yewon Jo1, Wontaek Ryu2, Hionsuck Baik1, Mino Yang1*
Affiliations : 1 Seoul Center, Korean Basic Science Institute, Seoul 02841, Korea; 2 Center for Inter-University Research Facility, Kookmin university, Seoul 02707, Korea
Resume : The dislocation studies on GaN, wide band-gap semiconductor of 3.4eV, have been performed for them normal to (0001). But in real the dislocation are inclined from <0001> especially where the strain varies distinctively. They are the area near the active layer where high amount of Si, Mg, In and Al are doped, and the case of GaN grown on Si (111). Jog or kink accompany when a dislocation is inclined, and the core structure of the dislocation would be deformed from them of parallel to <0001>. We studied the structure of the dislocation with the GaN grown on Si(111) using the transmission electronic microscopy techniques. In the BF view, most of the dislocation were characterized to be edge type. As the inclined angle is about 12 degree from <0001>, it is seen dislocation climb would happen frequently. We have changed the focus in STEM view and acquired a series of images with the respective focus, that is called optical sectioning. As the result, the structure similar to (0001) stacking fault was observed most frequently. And highly strained open-core dislocation also have been observed. In the side of electronic structure, the highly strained open-core edge dislocation might contain Ga metallic bond. From the present result, even it need be more deeply studied, there is great possibility that the inclined edge type dislocation introduce much severe defect-level in band gap degrading the efficiency of the GaN devices. (NRF-2016R1C1B1013667)
Authors : A.V.Gradoboev (1,2), K.N. Orlova (1), A.V. Simonova (1)
Affiliations : (1) National Research Tomsk Polytechnic University, Tomsk, Russia; (2) Joint-Stock Company “Research Institute of Semiconductor Devices”, Tomsk, Russia
Resume : For a long time light-emitting diodes (LEDs) based on gallium phosphide widely applied in optoelectronics. Furthermore, they stay advanced for modern optoelectronics devices manufacturing. Lack of full description of ionizing radiation influence on these LEDs limits their using. The purpose of this investigation is to research parameters changes of LEDs based on GaP epitaxial structure with 590 nm emission wavelength under irradiation by 60Co gamma-quanta. Irradiation was realized by 60Co gamma-quanta without imposition of external electric fields. Before and after irradiation volt-ampere (V-I) and watt-ampere (W-I) characteristics were measured. Based on LEDs V-I characteristics analysis the resistance of ohmic contacts for the investigated LEDs is equaled to (2.28±0.5) Ohm and it practically remains constant up to 2 MGy. W-I characteristics changes under irradiation allow to emphasize low, average and high electron injection fields. Dependences of boundary currents changes between the marked areas on irradiation doses are shown. Emissive power decrease of LEDs with gamma-quanta influence has three stages in the same way that it was observed for LEDs based on AlGaAs, AlGaInP heterostructures with multiple quantum wells. So, the emissive power drop under irradiation by gamma-quanta is described by similar mechanism for various types of LEDs based on different semiconductor structures.
Authors : I. Daldoul(a), N. Chaaben(a), I. Guizani(a), Y. El Gmili(b), A. Bchetnia(a), J. P. Salvestrini(b,c) and A. Rebey(a).
Affiliations : (a)Unité de Recherche sur les Hétéro-Epitaxies et Applications, Faculté des Sciences de Monastir 5019, Université de Monastir, Tunisia. (b)CNRS, UMI 2958 Georgia Tech - CNRS, 57070 Metz, France. (c)Université de Lorraine, Centrale Supelec, LMOPS, EA4423, 57070 Metz, France Corresponding authors. Tel: +216 73 500 274; fax: +216 73 500 578. E-mail: firstname.lastname@example.org
Resume : GaN layers were grown by metal organic vapor phase epitaxy (MOVPE) on GaAs (110) substrate at growth temperature varied in the range of 750-900°C. Low growth temperature (550°C) 50 nm-thick GaN layer was used as buffer layer. The characterizations results obtained by scanning electron microscope (SEM), high resolution X-ray diffraction (HRXRD) and room temperature cathodoluminescence (RT-CL) showed high growth temperature dependence of crystalline and optical properties of GaN. Mixture of cubic and hexagonal crystal structure of GaN were obtained on GaAs (110) surface. The 2?/? spectra are dominated by two broad peaks associated with c-GaN (220) and h-GaN(11.0) reflections. The better alignment of cubic GaN according to (220) orientation was obtained for growth temperature of 850°C. For this growth temperature, morphological observations by SEM showed columnar structure of c-GaN(220) that inclined with respect to the sample surface. The RT-CL spectra showed only cubic GaN emission for this sample whereas both emissions of c-GaN(3.23 eV) and h-GaN (3.40 eV) were observed for 900 °C as extreme growth temperature. Keywords: MOVPE, c-GaN(220), GaAs(110) substrate, HRXRD, Cathodoluminescence.
Authors : Aiwu Wang, Chris Lee, Haidong Bian, Zhe Li, Yawen Zhan, Jun He, Yu Wang, Jian Lu,* and Yang Yang Li
Affiliations : Department of Physics and Materials Science City University of Hong Kong
Resume : A silica- graphitic-C3N4-dots gels was prepared by a one-pot hydrothermal method, the obtained si-g-CDs gels can illustrates white light and has a highly quantum yield of 27% at 365 nm, better than most of carbon nanostructures reported before. The si-g-CDs can be used in White-LEDs and fluorenscent inks. Moreover, wearable device can be used due to its high color index and non-toxicity. The Si-g-CNDs gels also have excellent transparency and flexibility. This work presents a very facile way to fabricate a non-metal high efficiency white LEDs which have potential to largely scale synthesis and applied
Authors : Lana Lee, Baodan Zhao, Le Yang, William Lansbury, Dr Robert Hoye, Dr Dawei Di, Prof Judith Driscoll
Affiliations : University of Cambridge
Resume : Nickel oxide (NiO) is a wide band-gap p-type semiconductor which has attracted attention as a stable hole-transport/electron-blocking layer in organometal halide perovskite solar cells, demonstrating power conversion efficiencies of over 16%. However, the highest performing perovskite/NiO devices reported to date use NiO formed by vacuum deposition methods such as sputtering and pulsed laser deposition (PLD). Atmospheric pressure spatial atomic layer deposition (AP-SALD), developed in our group, involves the reaction of metal- and oxygen- containing precursor vapours which run through separate channels onto a heated substrate with controlled movement. This enables layer-by-layer deposition of a metal oxide film in air, removing the need for lengthy vacuum-processing steps whilst the technique can be potentially scaled up for high-throughput manufacturing. In this work, we demonstrate the deposition of high-quality NiO films by AP-SALD for the first time, with growth rates on the order of 2.5 Å/cycle. Pinhole-free films with <1 nm RMS roughness are achieved on glass with areas as large as 65 x 65 mm2, enabling reliable deposition of the subsequent perovskite photovoltaic absorbers. Our prototypical perovskite solar cells using AP-SALD NiO show promising power conversion efficiencies of over 12%. Additionally, the NiO films grow conformally to high aspect ratio substrates, making them compatible with textured silicon cell surfaces in tandem photovoltaic devices; a promising area of development for perovskite solar cells. The structural and electrical properties of AP-SALD NiO films will be presented in detail. Deposition conditions optimised for device applications will also be investigated. We will demonstrate the applicability of AP-SALD NiO films in high efficiency perovskite solar cells, for both individual cells and tandem structures.
Authors : A. F. Zatsepin, Yu. A. Kuznetsova, V. A. Pustovarov, M. A. Mashkovtsev, V. N. Rychkov
Affiliations : Ural Federal University, Mira st., 19, Ekaterinburg, 620002, Russia
Resume : Gadolinium oxide doped with rare-earth ions are of interest as functional material for nanophotonics, optoelectronics, alternative energy and conversion system devices. It is known that erbium ions are one of the most suitable emitters in green and red spectral regions. Moreover, specialties of structure of Er3+ energy levels provide an opportunity to convert of UV and near infrared radiation to visible light. The determination of optimal concentration of dopant is a key factor to achieve of highest energy conversion efficiency. The aim of this work is to investigation the luminescent behavior of nanostructured Gd2O3:Er as a function of different Er3+- concentration (0.25-8 mol%). To this purpose the quantum yields, kinetics, temperature dependences of Gd2O3:Er photo-stimulated luminescence under the direct (intracenter) and indirect (energy transfer from «defective» Gd3+-ions) excitation channels have been studied. The results allowed to discuss the nature of concentration quenching mechanisms and establish the quantitative composition of Gd2O3:Er – based materials for the enhancement of energy conversion parameters.
Authors : Donia Fredja (1), Chaouki Ben Hassen (1), Slim Elleuch (2), Habib Feki (2), Nassira Chniba (3) Boudjada, Tahar Mhiri (1), Mohamed Boujelbene (1)
Affiliations : (1) Laboratoire Physico-Chimie de l’Etat Solide, LR11 ES51, Faculté des Sciences de Sfax, Université de Sfax, BP 3071 Sfax, Tunisie; (2) Laboratoire de Physique Appliquée (LPA), Université de Sfax, Faculté des Sciences, BP 1171, 3000 Sfax, Tunisie (3) Laboratoire de Cristallographie, CNRS, 25 avenue des Martyrs, BP 166, 380, France
Resume : Organic–inorganic hybrid materials have been broadly investigated owing to their various properties used in optoelectronics and solar cell . Here, we report synthesis of two new organic-inorganic hybrid materials ([C10H10N2]2[Bi2Cl9]Cl and [C10H10N2]2[SbCl4]2Cl2) which are obtained by slow evaporation at room temperature using the same organic cation and two different metals. These two compounds are characterized by X-ray diffraction, infrared and Raman spectroscopy, optical absorption and photoluminescence measurements. Regards the first material, the atomic arrangement revealed that each inorganic entities shares two chlorine atoms to establish the neutrality of charges between anions and protonated cations, Hirshfeld surfaces analysis confirms that Hydrogen bonds dominates to make the stability of the crystal. The structure of the second compound, is formed by parallel layers of 2,2'-dipyridyl cations, anions of (SbCl4)- located in cavities between these layers and isolated chlorine atoms which make the building of the crystal. Hydrogen bonding interactions between anions and organic cations assure the stability of the structure. The assignment of the bands observed in infrared and Raman spectra were predicted from the calculated intensities which shows well agreement with experimental data. Additionally, we demonstrate that these compounds can be used in solar cells. In fact, the energy band gap of these materials was found to be closed to that used in interfacial layers  of some organic solar cells. By optimizing optical, electrical, and morphological properties of these new wide bandgap materials, bulk heterojunction solar cells with conversion efficiency exceeding 7 % are obtained in normal device structures with all-solution-processed interlayers.  Vitalii Yu. Kotov et al., New J. Chem., 2016, 40, 10041--10047  Sadok Ben Dkhil et al., Adv. Energy Mater. 2014, 4, 1400805
Authors : Benjamin A.D. Williamson(1), David O. Scanlon(1,2)
Affiliations : (1) University College London Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, UK ; (2) Diamond Light Source Ltd. Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK
Resume : The need for a high performance, earth abundant transparent conducting oxides (TCOs) is ever present in the expanding electronics and photovoltaics industry. TCOs possess large band gaps (> 3.2 eV) in order to avoid the absorption of visible light, resistivities as low as ~10^-5 ? cm as well as large carrier concentrations (~10^20 cm^-3). Arguably the flagship TCO material is In2O3:Sn (Tin doped Indium Oxide, ITO) with resistivities as low as 10^-5 ? cm making this material ideal for consumer electronics. A main limitation of this material however, is the high cost of indium and the rarity of the element in the earth?s crust which drives the search for a cheaper alternative. SnO2 is an obvious choice due to desirable properties such as high mechanical strength and environmental stability as well as possessing an ideal electronic structure. It is commonly found as the transparent contact layer in photovoltaics.(1) High conductivities can be achieved by doping with Antimony (Sb) or Fluorine (F) which are the most common choice for donor dopant in SnO2 resulting in resistivities as low as 10^-4 ? cm(1) similar to that of ITO yet these dopants are inherently self-limiting. In this presentation we detail the detrimental limitations of Sb and F doped SnO2 using accurate hybrid density functional theory (DFT) and give insights into new screened and intuitive donor dopants which do not succumb to the shortfalls of the past. (1) Bhachu, D. S.; Waugh, M. R.; Zeissler, K.; Branford, W. R.; Parkin, I. P. Chem. - A Eur. J. 2011, 17 (41), 11613.
Authors : Florian BARTEN, Martin WILHELM, Peter J. WELLMANN
Affiliations : Crystal Growth Lab, Materials Department 6 (i-meet), University of Erlangen (FAU), Martnesstr. 7, 91058, Erlangen, Germany
Resume : Among the various SiC polytypes, cubic 3C-SiC is much more difficult to grow in high crystalline quality than the state of the art hexagonal 6H-SiC and 4H-SiC counterparts. Beside some benefits of 3C-SiC for transistor applications related to a greater electron mobility and a lower metal-oxide-semiconductor interface trap density compared to 4H-SiC, new optoelectronic applications have been discussed in literature very recently. Boron doped 3C-SiC may act as an ideal candidate for an intermediate band (IB) solar cell material. Aluminum doped p-type 3C-SiC could lead to the development of efficient opto-electrochemical water splitting cells. Finally, 3C-SiC with its various intrinsic point defects has been is considered as a suitable candidate for future spintronic-applications. In the presented study we investigated free standing n-type and p-type 3C-SiC material grown in our lab. Temperature dependent photoluminescence measurements revealed the presence of carbon vacancy related V_C(+/++) and V_C C_Si (+/++) intrinsic point defects in the p-type material but not in the n-type materials. This observation is believed to have significant impact on the above mentioned optoelectronic applications.
Authors : Matthias ARZIG (1), TaChing HSIAO (2), Peter J. WELLMANN (1)
Affiliations : (1) Crystal Growth Lab, Materials Department 6 (i-meet), University of Erlangen (FAU), Martnesstr. 7, 91058, Erlangen, Germany. (2) Industrial Technology Research Institute of Taiwan (ITRI), 195, Sec 4, Chung Hsing Rd., Chutung, Hsinchu 31040, Taiwan
Resume : The morphology of the SiC powder source material during sublimation growth of SiC crystals has a great impact on the stability of the growth process in terms of constant growth conditions as well on the ability to grow long boules. In this work we studied the influence of three different SiC powder size distributions and the sublimation behavior in 3 inch growth configuration. The evolution of the source material as well as of the crystal growth interface was carried out using in-site X-ray computed tomography. Two SiC powders exhibited a single modal D90 size distribution of ca. 50 µm and ca. 200 µm, respectively. In both cases the average SiC powder density was 1.2 g/cm3. The third powder was a mixture of the above mentioned source materials and exhibited a bimodal particle size distribution. The corresponding average SiC powder density was 1.7 g/cm3. In this latter case the in-situ X-ray computed tomography study revealed an improved growth interface stability that enabled a much longer crystal growth process. During process time, the sublimation-recrystallization behavior of the mixed SiC powder showed a much smoother morphology change and slower materials consumption as well as much more stable shape of the growth interface than in the case of the less dense SiC source. By adapting the size distribution of the SiC source material we achieved to significantly enhance stable growth conditions. The latter is believed to be an important step towards a better polytype stability as well as towards a more constant dopant incorporation during bulk growth of SiC.
Authors : Bouaraba Fazia, Lamri Salim , Belkaid Mohamme Said.
Affiliations : Laboratoire Des Technologies Avancées Du Génie Electrique, Université Mouloud Mammeri de Tizi-Ouzou, Algérie. ICD-LASMIS, Université de Technologie de Troyes, UMR 6281, CNRS, Antenne de Nogent Pole Technologique de Haute-Champagne, France.
Resume : Transparent conducting oxide (TCO) films were widely used in optoelectronic devices such as electromagnetic shielding, gas sensors, information displays, and photovoltaic cells . Zinc oxide (ZnO) has been actively investigated as an alternate material to replace ITO due to its wide direct band gap (3.3 eV), an exciton binding energy of 60 meV , and other desirable properties such as low cost, abundance and nontoxicity. A few reports suggest that Titanium (Ti) is a possible dopant for ZnO films because Ti is a quadrivalent cation and has a radius of 68 pm which is closing to that of Zn (74 pm). The quadrivalent cation may provide one more valence than the trivalent cation as it substitutes Zn in ZnO films. Titanium-doped zinc oxide (TZO) films were prepared on glass substrates by DC magnetron co-sputtering using two individual Zn and Ti metallic targets in a mixture of oxygen and argon gases. Evolutions of the structural, morphological, electrical and optical properties of the TZO thin films were investigated by X-ray diffraction, UV–visible spectrophotometer, scanning electron microscopy (SEM) and four-point probe. The results show that all the films demonstrated strong preferential orientation and good electrical and optical proprieties. The optical constants such as absorption coefficient (α) and the optical bandgap (Eg) were determined from the optical transmission spectra
Authors : L.V. Borkovska1, L.Yu. Khomenkova1, I.V. Markevich1, M. Osipyonok1, M. Baran1, O. Marchylo1, M. Boisserie2, X. Portier2, T. Kryshtab3
Affiliations : 1) V. Lashkaryov Institute of Semiconductor Physics, 45 Pr. Nauky, Kyiv 03028, Ukraine; 2) CIMAP, Normandie Univ, ENSICAEN, UNICAEN, CEA, CNRS, 6 Blvd. Maréchal Juin, 14050 Caen, France; 3) Instituto Politécnico Nacional – ESFM, Av. IPN, Ed.9 U.P.A.L.M., 07738 Mexico D.F., Mexico.
Resume : Recently, transition metal Mn4 doped materials showing intense narrow red emission have attracted considerable interest due to their potential application as red-emitting phosphors in warm LEDs as cost-effective alternatives to rare-earth doped phosphors. Titanate compounds are known to be relatively cheap, easy-to-obtain and demonstrate excellent stability. Here we present the results of optical and structural investigations of lightly Mn doped magnesium titanate screen printed films and ceramics. The samples were produced through a traditional high temperature solid-state reaction method at 800-1150 °C using TiO2 and lightly Mn doped MgO powders as the raw materials. Electron spin resonance study showed Mn impurity to be about 1017 cm-3 in the raw MgO powder. The Raman spectra of the films showed that the formation of Mg2TiO4 with a cubic structure sets in at 900 °C. The evident red emission appeared in the films annealed at 1000 °C. In the photoluminescence (PL) spectra of the films, two sets of PL bands centered at 660 and 702 nm were observed. Corresponding excitation spectra consisted of two bands with maxima at 328 and 490 nm and at 335 and 542 nm. As the annealing temperature was increased from 1000 to 1150 °C, the intensities of the band at 660 nm in the PL spectra and the signals from Mg2TiO4 crystal phase in the Raman spectra increased. The intense red emission at 660 nm is ascribed to Mn4 in Mg2TiO4 phase, while the origin of 702 nm band is discussed.
Authors : Navadeep Shrivastava, Latif U. Khan, Jose M. Vargas; Carlos Ospina, Dinesh K. Shukla, Jose A.Q. Coeraqora,Yasir Javed, Hermi F Brito, Maria C. F. C. Felinto, Surender K. Sharma
Affiliations : Department of Physics, Federal University of Maranhão, Av. dos Portugueses, 1966 - Bacanga, São Luis - MA, 65080-805, Brazil. Department of Fundamental Chemistry, Institute of Chemistry, University of Sao Paulo, Av. Prof. Lineu Prestes, 748, 05508-000, São Paulo-SP, Brazil. Department of Neutron Physics, Bariloche Atomic Center,-Institute of Balseiro, Av. Exequiel Bustillo 9799, Bariloche San Carlos, Río Negro, Argentina. Advanced Materials Research Institute, University of New Orleans, 2000 Lakeshore Drive, New Orleans, LA 70148 Brazilian Nanotechnology National Laboratory (LNNano–CNPEM), Rua Giuseppe Máximo Scolfaro 10000, 13083-100, Campinas-SP, Brazil. UGC-DAE Consortium for Scientific Research, Indore Centre University Campus, Khandwa Road, Indore 452017, India Applied Physics Center, Institute of Physics, University of Brasilia, DF 70910-900 Brazil Department of Physics, University of Agriculture, Faisalabad, Pakistan Nuclear and Energy Research Institute - IPEN, University of Sao Paulo, Av. Prof. Lineu Prestes, 2242 - SP, 05508-000 São Paulo-SP, Brazil.
Resume : The ultra-small triply doped oleic acid coated hexagonal LaF3:xCe3 ,xGd3 ,yEu3 (x = 5; y = 1, 5, 10 and 15 mol%) nanoparticles were synthesized via a low cost non-aqueous polyol method. The XRD and HRTEM analysis confirmed the size between 5-7 nm. The FTIR measurement indicated chemi-absorbed coating of oleic acid. The auto-existence of Eu2 ions due to reduction was confirmed via XAS and detected by photoluminescence spectra. It had influence in emission property of LaF3:xCe3 ,xGd3 ,yEu3 nanomaterials, showing blue-white-red colors. The Judd-Ofelt parameters (Ωλ) were calculated extensively by intensities of the 5D07FJtransitions (J = 2 and 4) of the Eu3 ion and the forced electric dipole and dynamic coupling mechanisms are considered simultaneously. The greatest efficacy of 85% was achieved for the sample x= 5, y= 10 mol%. The luminescence decay profile suggest cross relaxation process in Eu3 ions when molar concentration of Eu dopant increased from 10 to 15 mol%. A energy transfer mechanism involving circulation of energy over Gd3 ion sub-lattice as bridge and finally trapping by Eu2/3 has been proposed. The DC susceptibility of the displayed ferromagnetically coupled behavior at low temperature. The materials have potential to act as multiplex detector, white LED and scintillators through downshift process, the reason being Ce3 /Eu2 as gamma ray sensitizer, Gd3 as highest stable neutron captor and Eu2 /Eu3 as luminescence activator in the visible region.
Authors : Qingbin Ji1, Tao Wang1, Wei Zhang2, Xixiang Zhang3,*, Xinqiang Wang1, Yahong Xie2,*, Xiaodong Hu1,*
Affiliations : 1 State Key Laboratory for Artificial Microstructure and Microscopic Physics, School of Physics, Peking University, Beijing 100871, China 2Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, United States 3Division of Physical Science and Engineering and Core Laboratories, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
Resume : III-Nitride compound semiconductors have attracted much interest and achieved tremendous progress in recent years. Conventional LEDs, LDs and other RF/power transistors are usually based on the six-fold symmetric hexagonal phase GaN (h-GaN). Moreover, h-GaN and related alloys possess high enough polarization fields (∼MV/cm) along the common growth direction <0001>, which are detrimental to transport properties, recombination efficiency and final device performance. However, these polarization fields don’t exist in cubic phase GaN (c-GaN). The biggest problem hindering the application of c-GaN is the phase instability, tending to transform into the more stable h-GaN. Thus, it is essential to achieve the stable existing c-GaN by some reliable growth methods . Here, we proposed a novel nano-scale-patterned Si(100) substrate with inverted-pyramid-shaped holes, by which we can obtain the maximum coverage of cubic-phase GaN. A 2inch-Si(100) wafer coated with patterned SiO2 film was selectively wet-etched in KOH solution. The diameter of the inverted-pyramid-shaped holes is around 300 nm and the sidewalls with Si(111) crystal faces were exposed. The growth of cubic GaN was conducted in a Thomas Swan MOCVD system using TMGa, TMAl and NH3 as precursors. AlN buffer was adopted to protect the Si substrate from the Si-Ga meltback phenomenon. The cross-sectional SEM image of GaN grown in the inverted-pyramid-shaped hole is shown in Figure 1a. The flat top surface of GaN grain is observed. The red and blue rectangles show the regions investigated under Titan-CsP probe-corrected STEM. Corresponding high resolution TEM images are seen in Figure 1c and 1f, Figure 1d and 1g. GaN in marked regions are both proved to be cubic-phase through the FFT diffraction patterns in Figure 1b and 1d. The diffraction peak at about 40° of the XRD (002)-plane 2θ-ω curve in Figure 1h, and the CL peak at 387 nm in Figure 1i also indicate the existence of c-GaN.
Authors : Tien-Chai Lin1, Wen-Chang Huang2*, Jyun-Yan Wu2
Affiliations : 1 Department of Electrical Engineering, Kun Shan University, No. 195, Kun-Da Rd., Yung-Kang Dist., Tainan, 71003, Taiwan, ROC 2 Department of Electro-Optical Engineering, Kun Shan University, No. 195, Kun-Da Rd., Yung-Kang Dist., Tainan, 71003, Taiwan, ROC *Corresponding author: Wen-Chang Huang (email@example.com)
Resume : Hydrogen sensor based on MgZnO thin film which was deposited by an RF co-sputtering is presented in the research. Both the MgO and ZnO targets are used to deposit the MgZnO film and its power toward is fixed at 100 and 125 W, respectively, with various times. The result shows a best sensing response of 2.46 for hydrogen concentration of 1000 ppm is obtained at the deposition time of 40 min with substrate heating at 300 C. The sensing response increase with the film thickness is due to the increase of oxygen vacancies which results from the defect of a thicker film. While, the sensing response decrease with further increase of thickness is due to grains growth. The x-ray diffraction analysis and the field emission scanning electron microscopy are also use to observe the film quality of the MgZnO thin film.
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Nitrides : Bettina Friedel
Authors : Saiful Alam1,2,3, Suresh Sundaram 2, Xin li 2, Miryam E. Jamroz 3, Youssef El. Gmili 2, Ivan C. Robin 3, Jean-Paul Salvestrini 2, Paul L. Voss 1,2, Abdallah Ougazzaden 1,2*
Affiliations : 1. School of Electrical & Computer Engineering, Georgia Institute of Technology, 30332, Atlanta, GA, USA. 2. Georgia Tech Lorraine; UMI 2958, Georgia Tech-CNRS, 57070 Metz, France. 3. CEA-LETI, Minatec Campus, F-38054 Grenoble, France.
Resume : InGaN/GaN based visible light emitting diodes (LEDs) are commercially successful and play a dominant role in solid state lighting . As a way to get white light emission for lighting applications, phosphor-based down-conversion results in low efficiency due to Stoke’s loss and also yields low colour rendering index (CRI) . Hence, to obtain high efficiency and high CRI white light, generation of white light by RGB combination is necessary. InGaN/GaN based blue LED has achieved good efficiency  and III-phosphides based red LED has also got high efficiency . However, at green emission wavelengths, the light emission efficiency of devices grown in the commonly used c-direction of GaN decreases with increasing indium (In) content in the active region . Primarily, this is attributed to the increased piezoelectric field in the InGaN/GaN quantum wells (QWs) under biaxial compressive strain that eventually leads to local separation of electrons and holes within the QWs and consequently decreases the emission efficiency . Even though growing stable semi-polar or non-polar planes  has received much attention to minimize the polarization problem, good crystal quality and processes that are mask-free and result in fewer processing steps make optimized structure design for c-direction growth still commercially promising. We have grown MQW structures by MOVPE in c(0001) direction on a ~70 nm thick high quality semi-bulk (SB) InGaN buffer (4 periods 15 nm InGaN and 2 nm GaN layers in between two successive InGaN layers) with InGaN barriers other than on conventional GaN buffer with GaN barriers and studied morphologically and optically in details. MQW with indium content of 5% - 7% in the buffer and barrier and 15% - 18% in the wells has yielded blue to cyan emission with a potential to extend to green emission by increased In. Our designed structure gives almost doubled optical emission along with a red-shift in emission wavelength compared to those of a conventional MQW structure. This improvement is due to the screening of built-in field by surface polarization field that eventually reduces the net built-in electric field and also due to more homogenous carrier distribution among the MQWs, when grown on semi-bulk InGaN buffer. These effects result in reduced band bending that increases the emission efficiency by more overlapping of electron and hole wave functions. Less droop is observed by simulation and a 67.5% internal quantum efficiency at an emission wavelength of ~480 nm has been experimentally obtained for MQWs structure with semi-bulk InGaN buffer and InGaN quantum barrier. Detail temperature and excitation power dependent photoluminescence (PL) experiments were carried out to explain the wavelength red-shift and band-filling scenario of localized carriers for our particular MQW in comparison with a conventional MQW. This detail analysis and study of photo excited luminescence is useful for realization of green-gap range emission by an InGaN/InGaN MQW using the semi-bulk InGaN buffer technique.  Daniel D. Koleske et al., Report of Sandia National Laboratories, Albuquerque, New Mexico 87185 and Livermore, California 94550, June 2013.  Auf Der Maur, M. et al., Physical Review Letters 116(2), 1–5 (2016).  Narukawa, Y. et al., Journal of Physics D: Applied Physics, 43(35), 354002 (2010).  Joachim Piprek, Physica Status Solidi (a), 207(10) 2217-2225 (2010).  T. Wunderer et al.,Physica Status Solidi (b), 248(3) 549-560 (2011).
Authors : Toshiya Yokogawa, Syota Miyake
Affiliations : Yamaguchi University, Department of Material Science and Engineering
Resume : Recently optoelectronic devices and electronic power devices using GaN-based materials have attracted much attention because they exhibit high optical and electrical power with high efficiency due to the wide band-gap. These power devices are generally used in high temperature operation by the heat dissipation. For high device reliability, it is important to design the mounting structure for heat sink to obtain efficient heat spreading. Carbon nanotube is expected to be excellent heat conductor for heat spreading because of extremely high thermal conductivity. Therefore, it is thought that carbon nanotube is very useful for electrode material with high thermal conductivity in the GaN device. Recently, we reported on the large workfunction of metallic multi-wall carbon nanotubes (MWCNTs). And we concluded that there is possibility to exhibit ohmic property to p-GaN. In this paper, we demonstrate low contact resistance of the MWCNTs ohmic contact to p-GaN film and LED operation with low voltage. We confirmed the work function of the metallic MWCNTs was determined to be 4.84 eV as high as that of Au, Pd and Ni which are generally used for the p-GaN contact. The specific contact resistance values of the MWCNTs/p-GaN interface were measured by the transfer length method. The MWCNTs electrode layer was prepared on the p-GaN. Finally, the specific contact resistance of the MWCNTs electrode was as low as 2.6×10-3 Ωcm2. We confirmed low contact resistance of the MWCNTs ohmic contact to p-GaN film. We also characterized the properties of LEDs using the MWCNTs ohmic contact for p-GaN. Low operation voltage was successfully obtained. Threshold voltage was about 2.7 V, and high optical power of about 1 W was also obtained.
Authors : Manjari Garg, Tejas R. Naik, Subramaniyam Nagarajan, V. Ramgopal Rao, Rajendra Singh
Affiliations : Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India; Department of Electrical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai-400 076, Maharashtra, India; Department of Micro and Nanosciences, Aalto University, P.O. Box 13500, FI-00076, Aalto, Finland
Resume : The present work aims to investigate the control of self-assembled monolayers (SAM) of Thiol- Porphyrin on the electrical characteristics of GaN based Schottky barrier diode (SBD). It has been reported earlier that the adsorption of SAM of organic molecules onto the semiconductor side or the metal side of the metal-semiconductor interface leads to the tuning of either the semiconductor work function or the metal-gate work function and hence tuning the barrier height in the SBD. This phenomenon may assist in overcoming the problem of Fermi-level pinning on different semiconductors, without regard to actual distribution of gap states. In this work, SAM of Thiolated Porphyrin (TTPSH) organic molecules were sandwiched between Copper (Cu) metal and Gallium Nitride (GaN) semiconductor to tune the work function. The chemisorption of TTPSH SAM on GaN surface was confirmed by using Water contact angle measurements, X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM). Kelvin Probe Force Microscopy (KPFM) revealed that the GaN surface potential was reduced from 950 mV to 750 mV after the adsorption of SAM on GaN. A decrease in the surface potential of semiconductor side of the metal-semiconductor interface implies decrease in work function of the semiconductor which may lead to an increase in Schottky barrier height. Cu metal was deposited on the molecularly modified GaN surface and was electrically characterized by current-voltage (I-V) measurements. A significant increase in Schottky barrier height and a decrease in reverse bias leakage current by four orders of magnitude was obtained. An increase in the photoluminescence (PL) intensity of GaN at 365 nm wavelength shows that surface passivation of GaN is occurring, which leads to the improvement of electrical characteristics of the diodes.
Authors : M. Vieira, M. A. Vieira, P. Louro, V. Silva, A Fantoni
Affiliations : Electronics Telecommunication and Computer Dept. ISEL, R. Conselheiro Emídio Navarro, 1959-007 Lisboa, Portugal ; CTS-UNINOVA, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal; DEE-FCT-UNL, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal;
Resume : A selector based on a tandem SiC wide band gap optical filter with near-ultraviolet steady states optical switches to select the visible wavelengths is presented. Spectral response and transmittance measurements are performed and show the feasibility of tailoring the wavelength and bandwidth of a polychromatic mixture of different wavelengths. Frequency dependence is analyzed. The selector is realized by using a two terminal double pi’n/pin a-SiC:H photodetector. Five communication channels having different wavelengths and bit sequences are transmitted simultaneously. The combined optical signal is analysed by reading out the photocurrent, under near-UV front steady state background. Data show that 25 different levels in the photocurrent are detected and correspond to the transmission of the thirty-two on/off possible states. The proximity of the magnitude of consecutive levels causes occasional errors in the decoded information. To minimize the errors, four parity bit are generated and stored along with the data word. Results show that the background works as a selector in the visible range, shifting the sensor sensitivity and together with the parity check bits allows the identification and decoding of the different input channels. A transmission capability of 60 Kbps was achieved. The relationship between the optical inputs and the output signal is established and an algorithm to decode the MUX signal presented. An optoeletronic model gives insight on the system physics.
Authors : Patrick Daoust, Patrick Desjardins, Remo Masut
Affiliations : Polytechnique Montréal, Génie Physique; Polytechnique Montréal, Génie Physique; Polytechnique Montréal, Génie Physique
Resume : Aluminium nitride (AlN) is a staple piezoelectric material used in the MEMS industry. Of particular interest is the use of this material in piezoelectric energy harvesting devices. Here we report the impact of the inclusion of rare earth elements (scandium, yttrium and lanthanides) in AlN as substitutionnal alloys. The d33 coefficients of AlN and its alloys were obtained with Ab-initio density functional theory simulations with Abinit and a SQS supercell. The 4f electrons of the lanthanides were represented with a large core in order to facilitate the calculations. The obtained d33 coefficients of the alloys vary from 28 pm/V for scandium to 12-18 pm/V for the lanthanides. We discuss how the elements impact this coefficient and how the use of alloys could benefit the energy harvesting efficiency of devices. We conclude that scandium bearing alloys present the most gain in terms of the electromechanical coupling factor and point out other requirements, such as resistivity of the material, for efficient AlN alloy harvesters.
Solar cells : Ole Martin Løvvik
Authors : Adam Zaba, Svitlana Sovinska, Elzbieta Nowak, Jerzy Sanetra, Katarzyna Matras-Postolek
Affiliations : Cracow University of Technology, Warszawska St. 24, Cracow, 31-155 Poland
Resume : Nowadays, the World need to face increasing demand for electric energy. Solar cells could be the alternative source of energy. It is really important to invent material, which would allow us to produce cheap solar cells with high efficiency. In this paper, the one dimensional (1D) ZnS nanocrystals were synthesized for PV solar cells based on poly(3-hexylotiophene) P3H. ZnS nanowires were obtained using zinc stearate, thiourea and octadecylamine (ODA) as a stabilizer and solvent. The obtained material was characterized with the use of XRD, FT-IR, NMR and TEM analysis. The ZnS nanowires have wurzite structure with diameter about of 20 nm. The surface of obtained nanocrystals was modified with derivatives of aminobenzene and aminonaphatlene. The products were characterized with the previously mentioned methods. The original ZnS nanorods and the ones obtained as a result of ligand exchange were used to produce solar cells with P3HT as a conductive polimer. Solar cells with 1D ZnS nanocrystals have a efficiency about 0,5%. This work was financially supported by National Centre for Research and Development under Lider Program, contract no. LIDER/009/185/L-5/13/NCBR/2014.
Authors : Faisal Baig,Yousaf H. Khattak ,Bernabé María,Hanif Ullah
Affiliations : School of Design EngineerinG, Departament of Applied Physics,Universitat Politècnica de València, Spain ; Department of Electrical Engineering,Federal Urdu University of Science, Arts and Technology,Islamabad, Pakistan
Resume : CuGaS2 / Cd1-xZnxS based solar cell is proposed in this research work. The performance of a solar cell is simulated and analyzed on simulation software called SCAPS. The structure of a photovoltaic cell is based on Cr doped CuGaS2 semiconductor as the absorber layer and n-dopped Cadmium Zinc Sulphide (CdZnS) as the buffer layer. Analysis is perform on different parameters such as the thickness of the CuGaS2 absorber layer and its carrier density, working temperature, Cd1-xZnxS buffer layer thickness and its carrier density to analyze their effects on the cell performance. The simulations show that the optimized thickness for the absorbing layer and the buffer layer should be from 0.1µm to 5 µm and 0.01µm to 0.7µm, respectively. The optimal photovoltaic properties has been achieved with an efficiency of 28.83% with FF= 84.19%, VOC = 1.0528 V and JSC = 32.52 mA/cm2 when the thickness and carrier density of the CuGaS2 is 2.7µm and 1 ×〖10〗^15 〖cm〗^(-3), respectively, the thickness and the carrier density of the Cd1-xZnxS is 0.5µm and 1 ×〖10〗^16 〖cm〗^(-3), respectively. The above results will give some important guide for feasibly fabricating higher efficiency CuGaS2 solar cells.
Authors : 1- Lamia Radjehi 2- Salim Laamri 3- Abdelkader Djelloul
Affiliations : 1- LASPI2A Laboratoire des Structures, Propriétés et Interactions Inter Atomiques, Khenchela University, Algeria and Université de Technologie de Troyes Antenne de Nogent-Pole Technologique de Haute champagne Rue Lavoisier, 52800 Nogent BP 41, France 2-Université de Technologie de Troyes Antenne de Nogent-Pole Technologique de Haute champagne Rue Lavoisier, 52800 Nogent BP 41, France 3- a LASPI2A Laboratoire des Structures, Propriétés et Interactions Inter Atomiques, Khenchela University, Algeria
Resume : Copper oxide (CuxO) thin films have many applications in heterojunction solar cells, electrochromic devices, oxygen and humidity sensors and attracted significant attention owing to their excellent properties including high absorption coefficient, non-toxic nature and low cost production. The aim of this work is to study the effect of the oxygen flow ratio on the electrical, optical, structural and morphological properties of copper oxide films deposited on Silicon and glass substrates using direct current (DC) reactive magnetron sputtering. The results showed that The crystalline orientation and film's properties were dependent on the oxygen flow ratio and annealing temperatures. A better crystallinity of cuprite and tenorite deposited at the oxygen flow ratio of 20 sccm and 35 sccm respectively was observed and confirmed by photoluminescence. In order to study the morphology of the grown structures a field emission scanning electron microscope was used. The phase structures of films were investigated by X-ray diffractometer. The electrical and optical properties were systematically investigated using Optical absorption UV–visible, four-point probe methodand photoluminescence (PL)
Authors : Sakuchika Sakai, and Kousaku Shimizu
Affiliations : Graduate School of Industrial Technology, Nihon University
Resume : We have been investigating wide gap solar cells for the top of a tandem solar cell. Processing at low temperatures, which allows the use of glass substrates, is to be beneficial for the applications in terms of lowering the fabrication cost. We employed p-type Cu-Al-O (CAO) and n-type In-Ga-Zn-O (a-IGZO) as active layers. The pulse DC sputtering is performed on a glass substrate in 0-40% oxygen diluted argon atmosphere at temperatures as low as 250°C. The devices were annealed at less than 400°C in air for one hour. The optical band gap of a-CAO and a-IGZO is ~1.95 eV and ~3.21 eV, respectively. ITO/a-CAO/a-IGZO/ITO/substrate solar cells were fabricated and inverted structure solar cells (ITO/a-IGZO/a-CAO/ITO/superstrate) were fabricated for comparison. The light was illuminated from the p-layer side. I-V characteristics and conversion efficiency were quite different between substrate and superstrate cell. The maximum efficiency was around 0.87% under the AM1.5 illumination for substrate type and that of the superstrate was about 0.19%, which was mainly caused by the interface defects. According to a device simulation, a large amount of interface defects in the superstrate cell still remained even after annealing at 380°C. From the modulated admittance method, the main defects located at above 100-150 meV from the a-CAO valence band edge. Although the poor performance of the solar cell, we have demonstrated the possibility of all sputtered top cell.
Authors : Gustavo Baldissera, Clas Persson
Affiliations : Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden; Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden, Department of Physics, University of Oslo, P.O. Box 1048 Blindern, NO-0316 Oslo, Norway,
Resume : The alloying of ZnO with GaN can substantially reduce the band gap, allowing the material to absorb in the visible light region. In this work we further investigate ZnO-GaN alloys in order to better understand the optical properties to allow an optimization of the material for solar energy usage. Our theoretical analyses are based on the density functional theory (DFT), and we improve the energy gaps by means of the meta-GGA modified Becke-Johnson exchange potential and also the post-DFT approach of HSE hybrid functionals . Pair distribution over the several used cells and concentration were analyzed. A correlation of the ratio of Ga-N (or Zn-O) bonds with the total energy was found, indicating that bonds favoring the proper valence match provide more stability. The dielectric function and absorption were analyzed. In the alloy, the onset for the absorption of light with respect to the band gap presents a change when in comparison to the binaries, leading to an optical band gap higher than the one obtained from the band structure. This can help to explain the differences found in different experimental methods . References:  M. Dou et al., J. Crystal Growth 350(2012).  K. Lee et al, J. Mater. Chem. A 4,2927 (2016).
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Ørsteds plads, building 343, 2800 Kgs. Lyngby, Denmarkhaou@fotonik.dtu.dk
Department of Physics, Chemistry and Biology, 58183 Linköping, Swedenmikael.firstname.lastname@example.org
SINTEF Materials and Chemistry, Forskningsveien 1, 0314 Oslo, NorwayOleMartin.Lovvik@sintef.no
Department of Materials Science and Engineering, 1-501 Shiogama-guchi, Tenpaku, Nagoya 468- 8502, Japanskami@meijo-u.ac.jp