bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Na Incorporation on Electronic Structures of p-Type Cu-deflcient CuInS2 Crystals
Authors: Yamamoto Tetsuya , Watanabe Takayuki
Published: March 2014

We have investigated the effects of intentional sodium incorporation on the electronic structures and electric properties of Cu-deflcient CuInS2 thin films. From ab-initio electronic band structure calculations, for p-type Cu-deficient CuInS2 films, we find that interstitial Na species, except for Na at Cu sites (NaCu), are very unstable and move easily within the crystal. On the other hand, we find that the formation of the ionic chemical bonds of NaCu-S atoms near the surface are energetically favorable due to a remarkable decrease in Madelung energy compared with that of neutral defects-complex of InCu-2VCu. Those calculated results indicate that controlled Na incorporation into CuInS2 thin films causes a decrease in the concentration of intrinsic donor defects such as InCu and VS, leading to good p-type conductivity of CuInS2 films. Those findings are in good agreement with experiments of electrical conductivity and photoluminescence.
Shape Memory Property and Electronic Structures of Films of Alloys Ni2+xMn1-xGa
Authors: Ishida Shoji , Sugimura Shinichi , Nagayoshi Hideo , Asano Setsuro
Published: March 2014

To study the effect of the surface on the shape memory and magnetic properties, we calculated the electronic structures of the films of Ni2xMn1-xGa. Comparing the total energies for the cubic and the tetragonal structure, we found the tendency that the shape memory property may not be preserved in thin films but is recovered with increasing thickness or increasing Ni composition. It was also found that the magnetic moments on Mn are largely enhanced at the surface.
Transport properties of p-type CuInSe2
Authors: Rogacheva Elena I. , Tavrina Tat'yana V.
Published: March 2014

Measurements of the Hall coefficient RH and electrical conductivity σ on the p-CuInSe2 polycrystalline samples with various Se content (50.0; 50.5 and 51.5 at.% ) at fixed cation ratio [Cu]/[In]=1.0 have been carried out in the temperature range of 77-300 K. On the basis of the RH temperature dependences the existence of two acceptor levels with activation energies of ∼ 19 meV and 72 meV has been established. The shallow level is supposedly connected with the Cu vacancies (VCu) while the deeper one is attributed to vacancies of In (VIn) and/or Se interstitials (Sei). Predominant mechanisms of hole scattering by ionized defects in the low-temperature region and by acoustic phonons in the high-temperature range have been determined using the temperature dependence of Hall mobility (µH). It has been shown that growth in the Se content and, consequently, the concentration of intrinsic defects leads to decrease in RH, σ and µH values. For the sample with maximum Se content (51.5 at.%), oscillations in the temperature dependences of RH and µH have been detected. It is suggested that these effects are connected with relaxation processes, i.e. with transition of rapidly cooled system to equilibrium state.
Observation of Record Electron Hall Mobility in CdGeAs2 Single Crystals
Authors: Rud' Vasilii , Rud' Yurii , Polushina Ida , Ushakova Tatiana , Iida Seishi
Published: March 2014

CdGeAs2 single crystals were prepared by low temperature crystallization from the nonstoichiometric melt. The temperature dependences of the electrical conductivity and the Hall coefficient were examined for CdGeAs2 single crystals. All the as-grown crystals show n-type conductivity with free electron concentration of 1018 cm-3 and Hall mobility of around 10000 cm2/(Vs) at room temperature. The Hall mobility increases with the temperature decrease and reaches 36000 cm2/(Vs) at 77 K. This is the first evidence of the high electron mobility for CdGeAs2 single crystals.
Cd0.8Mn0.2Te:(In/Al) - DLTS study
Authors: Placzek-Popko E. , Szatkowski J. , Sieranski K. , Fialkowski J. , Hajdusianek A. , Wrobel J. M. , Becla P.
Published: March 2014

Electron traps in indium and aluminum doped Cd0.8Mn0.2Te were studied with Deep Level Transient Spectroscopy. In indium doped Cd0.8Mn0.2Te, five electron traps were observed with activation energies of 0.23eV, 0.28eV, 0.38eV, 0.48eV and 0.65eV. In the material doped with aluminum, three electron traps were found with activation energies equal to 0.36eV, 0.47eV and 0.76eV. Defects, strongly coupled to the surrounding lattice, have been observed only for the indium doped samples. Two of the traps observed in the material are related to the defects with thermally activated capture cross sections of energy barrier for capture equal to 0. 14eV and 0.l8eV, respectively. Binding energies of related defects are equal to 0.09eV and O. l8eV. Both defects exhibit DX center characteristics.
Defect Distribution of CuInS2 Solar Cells from Different Preparation Processes as Determined by Admittance Spectroscopy
Authors: Siemer Kai , Kneisel Jochen , Luck Ilka , Klaer Jo , Scheer Roland , Klenk Reiner , Bräunig Dieter
Published: March 2014

Admittance spectroscopy measurements are carried out to determine the defect spectra of CuInS2 solar cells from different preparation methods. Different defects are found and partly interpreted in terms of interface and bulk defects with the help of annealing experiments and DLTS measurements. A correlation between defect spectrum and open-circuit voltage is found.
We further examine the origin of series resistances that influence the measurement of capacitance.
Natural Photopleochroism Oscillations in n-p-CdSiAs2 Homojunctions
Authors: Rud' Vasilii , Rud' Yurii , Serginov Meret , Iida Seishi
Published: March 2014

The photoelectric properties of n-p-CdSiAs2 homojunctions have been studied in natural and linearly polarized light. A fine structure consisting of one or two peaks is found for the first time in room temperature photoconversion efficiency spectra. Each of the peaks having splitting around 10 meV in the spectra is predominant in a certain polarization. The short-wavelength shift of the structure with decreasing temperature corresponds to the temperature shift of the CdSiAs2 energy band gap. It is suggested that the long-wavelength photosensitivity edge is of an exciton nature. It is established that oscillations arise in the natural photopleochroism spectra in this case.
Oscillations of Induced Photopleochroism in Obtained by Heat Treatment Process CuInSe2 Structures
Authors: Rud' Vasilii , Rud' Yurii , Schock Hans-Werner , Iida Seishi
Published: March 2014

The photosensitivity structures prepared by heat treatment in vacuum and air of p- and n-CuInSe2 polycrystalline substrates at 500°C are investigated and spectral dependences of photosensitivity of the prepared structures in natural and linearly polarized radiation are analyzed. The photosensitivity of such structures in connection with conditions of their preparation are discussed. Induced polarization photosensitivity was observed, and peculiarities of this phenomenon caused by antireflection effect in the thin films of these structures are discussed. A conclusion is made that polarization photoelectric spectroscopy has a new opportunity of application for diagnostics of photovoltaic devices.
Crystals and Thin Films of Zn2-2xCuxInxSe2 Solid Solutions: Structural and Physical Properties
Authors: Gremenok V. F. , Schmitz W. , Bodnar I. V. , Bente K. , Doering Th. , Kommichau G. , Victorov I. A. , Eifler A. , Riede V.
Published: March 2014

Zn2-2xCuxInxSe2 crystals were synthesized by the directional freezing method using elementary components as starting materials. The crystals were also used as target materials. Thin films of Zn2-2xCuxInxSe2 were prepared for the first time by pulsed laser deposition using a Nd:YAG laser and glass substrates at temperatures in the range 470 – 490 °C. The growth conditions of these samples and their composition, structural, electrical and optical properties have been studied. Especially the copper rich Zn2-2xCuxInxSe2 materials were investigated.
Band Gap Energies and Lattice Vibrations of the Lithium Ternary Compounds LiInSe2, LiInS2, LiGaSe2 and LiGaS2
Authors: Eifler Andreas , Riede Volker , Brückner Jaqueline , Weise Sylvia , Krämer Volker , Lippold Gerd , Schmitz Werner , Bente Klaus , Grill Wolfgang
Published: March 2014

The band gap energies EG of the lithium compounds have been measured by transmittance and reflectivity measurements as well as measurements of the diffuse reflectivity. At room temperature EG=2.83 eV (LiInSe2), EG=3.56 eV (LiInS2), EG=3.13 eV (LiGaSe2) and EG=3.62 eV (LiGaS2) have been obtained presupposing a direct interband transition. In a first attempt the birefringence of LiInS2 was studied by transmittance measurements. Using infrared and Raman spectroscopy the lattice vibrational properties have been investigated.
Probing the Interface and Microstructures in CdS/CuInSe2 and InGaAsN/GaAs Heterojunctions by Synchrotron Radiation
Authors: Soo Y. L. , Huang S. , Kao Y. H. , Deb S. K. , Ramanathan K. , Takizawa T.
Published: March 2014

Measurements of angular dependence of x-ray fluorescence (ADXRF), x-ray absorption fine structure (XAFS), and grazing incidence x-ray scattering (GIXS) using synchrotron radiation were utilized to study the migration of constituent atoms, microstructures, and interface morphology in two sets of heterostructures consisting of CuInSe2(single crystal)/CdS and InxGa1-xAs1-yNy/GaAs compounds. Both systems are useful for the development of innovative high efficiency solar cells. By comparing the ADXRF and XAFS data of a CdS-coated and a bare CuInSe2 single crystal, changes in the depth profile of atoms and their local structures due to CdS coating can be investigated with well-defined stoichiometry. Our results indicate that both Cu and Se atoms have migrated into the CdS layer in the heterojunction while In atoms remain practically intact in the CuInSe2 single crystal. For a study of the InxGa1-xAs1-yNy system, our XAFS results show a sp3 hybridized bonding configuration for N atoms, indicating that the N impurities most likely substitute for As sites in the compounds GaAs1-yNy and InxGa1-xAs1-yNy. Within experimental uncertainties, the results of In K-edge XAFS indicate that the In-As interatomic distance remains essentially the same as in InAs. Further, GIXS measurements confirm that In0.08Ga0.92As0.97N0.03 thin films can indeed form very smooth interfaces with GaAs.
Temperature Dependence of the Fundamental Absorption Edge in Cu2GeSe3
Authors: Marcano G. , Nieves L. , Perez G. S.
Published: March 2014

The temperature dependence of the energy gap EG in Cu2GeSe3 has been obtained from optical absorption measurements in the temperature range from 10 to 300 K. The data were analyzed by considering several models for the variation of EG vs. Treported in the literature. The best fit was obtained by using an expression proposed by Pässler [Phys. Status Solidi B 200, 155 (1997)]. From the analysis, the Debye temperature of this compound was estimated to be around 170 K. It is also obtained that the effective energy of phonons participating in the band gap shift with temperature is about 15 meV and correspond to the acoustic phonon branch.
Dielectric Function Spectra and Intraband Density-of-States in TlSe
Authors: Yamazaki Makoto , Toyota Hideyuki , Aoki-Matsumoto Tamao , Kerimova Elmira , Kato Ariyuki , Yamamoto Nobuyuki , Mamedov Nazim , Iida Seishi
Published: March 2014

Room temperature spectroellipsometric study of TISe was performed in the photon energy region 1.5-4.6eV. The tensor components of the dielectric function spectrum of TlSe were obtained. Interband density-of-states (DOS) derived from XX (YY) and ZZ components of the obtained dielectric function spectrum was then compared with the calculated intraband DOS, taking into account for selection rules and transition probabilities. It is found that contribution of the interband optical transitions in Γ, T and N points quite plausibly explains main structures in the obtained dielectric function spectra. However, some structures cannot be explained due to optical transitions in these symmetry points. A corresponding assignment is given and discussed.
One-Phonon Spectra and Effective Phonon Density-of-States in CaGa2S4
Authors: Mamedov Nazim , Iida Seishi , Aoki-Matsumoto Tamao , Kato Ariyuki , Yamazaki Makoto , Yamamoto Nobuyuki , Shishido Toetsu , Iwai Kazutoshi
Published: March 2014

Room temperature Raman study of the crystalline and amorphous CaGa2S4 was done. Stokes and Anti-Stokes spectra were obtained in back-scattering geometry using a high rejection double monochromator and the 5 14.5nm line of an argon ion laser. Except for polarization characteristics, the Raman spectra of the polycrystalline CaGa2S4 represent one-phonon spectra at the center of the Brillouin zone. The spectra consist of 18 lines rather than 84 Raman-active lines given by the factor-group analysis. The distribution of the one-phonon density-of-states from ω
min
=74.7cm-1 to ω
max
=4 12.7cm-1 exhibits a frequency gap between 199.8 cm-1 and 284.7cm-1. The effective phonon density-of-states across the Brillouin zone, which was derived from the Raman spectrum of the amorphous CaGa2S4, exhibits somewhat different distribution of the peak densities compared to one-phonon spectra. The upper limit for Debye approximation in CaGa2S4 is found at 21.7 cm-1. The applicability of the molecular approach to the Raman spectra of CaGa2S4 is discussed. It is proposed that two different structural units generate the most intense 284.7cm-1- and 360.7cm-1 -vibrations above the frequency gap.
Raman Spectra of Defect Stannite Phases in the Cu-(In,Ga)-Se System
Authors: Nomura Shigetaka , Endo Saburo
Published: March 2014

Lattice vibration behaviors of defect stannite phases in the Cu-(In,Ga)-Se system are studied by the Raman spectrometry and the dispersion curve calculation in comparison with the chalcopyrite phases in this system. Bulk crystals in the alloy systems of Cu(In1-xGax)3Se5 and Cu2(In1-xGax)4Se7 are prepared by the normal freezing method. The characteristic two Raman peaks at 160 and 175 cm-1 for these crystals, apparently unrelated to the indium to gallium ratio, are assigned as two Γ1 modes of D
2d
symmetry. This can be explained from the dispersion curve calculation assuming the vacancies at 2a or 2b site of the defect stannite structure through the Cu-(In,Ga)-Se system.
A Photoluminescence Study of Hydrogen-Implanted Cu(InGa)Se2 Thin Films
Authors: Yakushev Michael V , Martin Robert W , Urquhart Fiona , Mudriy Alexander V , Schock Hans W , Krustok Juri , Pilkington Richard D , Hill Arthur E , Tomlinson Robert D
Published: March 2014

Cu(InGa)Se2 (CIGS) thin films deposited on Mo-coated soda-lime glass substrates by co-evaporation, were implanted with H+ (2.5keV, doses from 1014 to 1017cm-2) at room temperature. Implanted and non-implanted areas of the films were characterised using photoluminescence (PL) at 10K. The PL spectra from non-implanted areas showed a broad band at 1.13eV (Al) and a long, low energy and low intensity tail with a well-defined band at 0.78eV. Implantation with up to 1015 cm-2 increased the intensity of band Al. Higher doses resulted in a reduction of the band intensity. Also three high intensity low energy peaks were observed in the PL spectra after implantation. One of the peaks was detected at 0.78eV. A high value of the blue shift for the excitation intensity dependence of band Al before the implantation suggested recombination through conduction and valence band tail states. After implantation the blue shift was found to decrease, it is assumed that the implanted H passivates some of the charged defect states in the band tails.
Excitonic Photoluminescence from CuGaSe2 Single Crystals and Epitaxial Layers: Temperature Dependence of the Band Gap Energy
Authors: Bauknecht Andreas , Siebentritt Susanne , Albert Jürgen , Tomm Yvonne , Lux-Steiner Martha Christina
Published: March 2014

Excitonic line spectra from CuGaSe2 single crystals and epitaxial layers are investigated as a function of temperature. Near band edge luminescence from free and bound excitons is observed at 10 K. The identification of both, free exciton ground and first excited state allows to determine the free exciton binding energy, which is found to be (13±2) meV. The bound exciton line is attributed to the recombination of an exciton bound to a neutral acceptor (A0, X). The widely discussed phenomenon of an anomalous temperature dependence of the band gap energies in different chalcopyrite-type I-III-VI2 compounds is reconsidered for CuGaSe2 on the basis of temperature dependent photoluminescence studies. No anomalous behaviour of the band gap energy as a function of temperature is found in CuGaSe2.
Exciton structures of single- and polycrystalline CuInSe2 and CuGaSe2
Authors: Chichibu Shigefusa F. , Mizutani Tsutomu , Nakanishi Hisayuki , Niki Shigeru , Fons Paul J. , Yamada Akimasa
Published: March 2014

Excitonic resonance energies of CuInSe2 and CuGaSe2 were shown to be greatly affected by the residual lattice strain. A clear excitonic absorption peak was found in high-purity CuGaSe2 polycrystalline thin films even at room temperature, showing the contribution of excitons in optical processes in chalcopyrite semiconductors.
Cooling Process of Hot Excitons in Ordered Ga0.5In0.5P
Authors: Kita T. , Sakurai M. , Yamashita K. , Nishino T. , Geng C. , Scholz F. , Schweizer H.
Published: March 2014

Time-resolved photoluminescence (PL) spectroscopy has been performed to investigate hot-exciton relaxation process in long-range ordered Ga0.5 In0.5 P. The cooling process of excitons shows strong order parameter dependence. The rise time of the exciton PL is getting faster with increasing degree of ordering. This indicates that optically created excitons rapidly relax in a fluctuated potential of the partially ordered epitaxial film. The exciton-PL lifetime becomes small with increasing order parameter. Also, the PL of ordered Ga0.5 In0.5 P exhibits a localized exciton feature with an much slower decay. These findings suggest that excitons tend to localize in ordered domain structure and can relax into localized deep centers via the nonradiative recombination pass in the ordered domain ensemble.
Deep Level Photoluminescence in CuIn1-xGaxSe2
Authors: Krustok Jüri , Raudoja Jaan , Yakushev Michael , Pilkington Richard , Hill Arthur , Collan Heikki
Published: March 2014

Deep level photoluminescence (PL) bands are studied in CuIn1-xGaxSe2 solid solutions at T=8K. These PL bands had peak positions at 0.4-0.5 eV below the bandgap energy Eg, In CuInSe2 these bands have a peak position at hν ≈ 0.58 eV and in CuGaSe2 they can be found at hν ≈ 1.1 eV. The energy of these deep PL bands shifts with the In/Ga ratio in the same way as Eg. It is shown that these bands arise from recombination within deep donor-deep acceptor pairs, where the donor defect is probably an interstitial copper and the acceptor defect is VIn or VGa.
Spectral Distribution of Photoemission Quantum Efficiency for Gex(As2Se3)1-x Glasses
Authors: Shchurova Tatiana , Savchenko Nicolai , Spesivykh Alexander , Baran Nicolai
Published: March 2014

The photoemission threshold energy for Gex(As0.4Se0.6)1-x(x = 0, 0.1, 0.2, 0.3) glasses has been derived from the spectral distribution of the photoemission quantum efficiency in the near-threshold region. Glass densities and optical band gaps have been measured. The top of the valence band has been calculated by the linear combination of atomic orbitals method and is in quantitative agreement with photoemission threshold value for the glasses under investigation. The changes in the optical band gap have been found to be related to the changes in the top of the valence band. The peculiarities of the concentrational dependences for the top of the valence band have been considered.
Effect of Stoichiometric Deviations on the Structural Properties of CuInSe2, CuIn0.5Ga0.5Se2 and CuGaSe2.
Authors: Díaz Raquel , Merino José Manuel , León Máximo , Vidales José Luis Martín De , Rueda Fernando
Published: March 2014

Ingots of CuInSe2, CuIn0.5Ga0.5Se2 and CuGaSe2 were synthesized under similar fusion at 1150°C in silisa ampoule, cut into slices and determined their composition by energy dispersive analysis of X-Rays. The structural properties, including the occupation fraction of each atomic sublattice, were studied by X-ray powder diffraction and Rietveld refinement. The Cu occupation number, N(Cu), is lower than one, The complex of two Cu vacancies and a substitutional catio, 2V(Cu)+B3+
Cu (B3+
Cu= In, Ga+In and Ga in CIS, CIGS and CGS respectively in a Cu site) is assumed and would explain the presence of Cu vacancies and allow an estimate of the B3+ concentration in its sublattice. When this increases a decrease in concentration of both Cu in its sublattice and the complex 2V(Cu)+B3+
Cu are found. The strucutrual parameters depend on Cu and B3+ sublattice occupancy fractions for all compounds..In CuGaSe2, the lattice parameters increase as does Ga3+(subl) while the opposite arrives in CuInSe2 for In3+(subl). The distance of Se atom to z axis depends on Cu(subl) for all the compounds increasing in the case of CuInSe2 with V(Cu) and InCu antisites, decreasing the InSe bond distance. The opposite effect is observed in CuIn0.5Ga0.5Se2, and CuGaSe2.
3-D Imaging and Analysis of Manganese Distribution in Zn1-xMnxIn2S4 by Laser Confocal Microscopy and Spectroscopy
Authors: Medina Honorio , Joshi Narahari
Published: March 2014

In manganese based ternary and multinary semiconducting compounds, and many photonic devices, the knowledge of the distribution of fluorescent species is a very important aspect both from theoretical and technological points of view. Laser confocal fluorescence microscopy together with confocal spectroscopy have been found to be the most adequate techniques as they permit to make optical sections at desired separations and reconstruct 3-D imaging of the crystal. We have, therefore, carried out such investigation for Zn1-x,Mnx,In2S4 compound and imaged the distribution of manganese. The identification of Mn++ was carried out by confocal spectroscopy which also reveals the precise location of Mn++ and /or other fluorescent species.
Magneto Optical Studies on the Origin of Shallow Bound Exciton Lines in CuGaS2
Authors: Matsumoto-Aoki Tamao , Shimojo Takahiro , Kumakura Hiromichi , Kato Ariyuki , Uchiki Hisao , Iida Seishi
Published: March 2014

The Zeeman effect on two absorption lines in CuGaS2 has been investigated for the first time for I-III-VI2 chalcopyrite semiconductors. Both of these absorption lines split into two components in a magnetic field where the magnetic field was perpendicular to the crystal c-axis. These splittings exhibited the same linear dependence on magnetic field, reaching about 1.1 meV at 5 T. These splittings can be described with apparent g value of about 4. Additional lines whose peak energies were close to those in zero-magnetic filed appeared in a magnetic field where the angle between magnetic field and crystal c-axis was 35°. The intensities of the lowest energy lines of these split lines decreased with a decrease of temperature in both configurations. The observed behavior is shown to be well explained with the model of excitons bound to neutral centers.
Growth and Crystallographic Properties of II – III2 – VI4 Compounds – Focusing on the Sulfides –
Authors: Takizawa Takeo , Komatsu-Hidaka Chiharu , Asaka Kimitaka , Isomoto Tokuyuki , Matsushita Hiroaki
Published: March 2014

Cd and (Ca,Sr) based II-III2-VI4 compounds are studied by focusing on the structural change caused by the exchange of the constituent atoms. First, the phase diagrams of CdGa2S4 – CdIn2S4 (cation exchange) and CdIn2Se4 – CdIn2S4 (anion exchange) are constructed with the help of the differential thermal analysis (DTA) and powder X-ray diffraction (XRD). In the case of cation exchange, phase transition from tetragonal to spinel through layer structure has been carefully studied as a function of the ratio of In to (In + Ga). Mixed phases with layer structure are observed in both sides of the phase diagram. Single layer phase is realized in a limited narrow region. On the contrary, in the anion exchange, clear phase separation occurs, i.e., phase mixing is observed only in a narrow region and three phases appear rather independently.
Secondly, to investigate the crystal structure on the exchange of IIb atoms with IIa atoms, Ca and Sr thiogallates are selected as target materials, and first the phase diagrams of (Ca,Sr)S – Ga2S3 are constructed. Based on these phase diagrams, single crystals are grown and their crystal structures are investigated in terms of the rietveld analysis.
Electrooptical Properties of InGaAs/GaAs Strained Single Quantum Wells
Authors: Lua Chien-Rong , Lou Shry-Fong , Cheng Hung-Hsiang , Lee Chien-Ping , Tsai Fu-Yi
Published: March 2014

The electrooptical properties of (100) and (111)B InGaAs/GaAs strained single quantum wells have been studied by the photoreflectance spectroscopy at various temperatures and under different biases. There is a Si δ-doping sheet under the GaAs surface to screen the surface built-in electric field from the quantum well. The spectral features consist of the excitonic interband transitions in the quantum well, and the Franz-Keldysh oscillations from the band edge transitions of the GaAs barrier near the surface. The piezoelectric field tilts the (111)B single quantum well toward the δ-doping and causes subband filling by the electrons from the δ-doping centers. With a proper external bias to repel electrons from the tilted quantum well, the excitonic interband transition in the (111)B system is enhanced.
Anisotropy of Optoelectronic Properties and Atomic Ordering in CdGeAs2
Authors: Bairamov Bahish H. , Fernelius Nils , Irmer Gert , Monecke Jochan , Polushina Irina K. , Pandey Ravy , Rud' Vasilii Yu. , Rud' Yurii V. , Schunemann Peter G. , Ohmer Melvin C.
Published: March 2014

Inelastic light scattering by optical phonons as well as temperature dependent electrical conductivity, Hall constant and photosensitivity were studied in ordered chalcopyrite structure CdGeAs2 crystals grown by ultra-low gradient freeze technique from near-stoich iometric melts.
Optical sensors sensitive to the light polarization: Phenomenological consideration through electronic parameters
Authors: Medvedkin Gennadiy A.
Published: March 2014

The polarization coefficient dependences on a depth of embedding p-n junction, diffusion length of minor charge carriers, surface recombination rate and lifetime of the carriers have been derived and analyzed numerically for optical sensors sensitive to the light polarization. The characteristic electronic parameters are shown to change dramatically the magnitude and sign of photopleochroism coefficient.
New Class of Heterojunctions Based on the Ternary Semiconductors
Authors: Rud' Vasilii , Rud' Yurii , Shpunt Vladimir , Iida Seishi
Published: March 2014

A photovoltaic effect at the semiconductor/natural protein junction has been discovered. We have created new-generation photosensitive structures based on liquid natural protein and semiconductors. For the first time the photoelectric parameters of semiconductor/protein systems have been investigated. We conclude that the new-class heterojunctions can be used as photoconverters of the natural and linearly-polarized light.
High-Efficiency AlGaAs/InGaAs/GaAs Pseudomorphic High-Electron-Mobility Transistors Using a Sub-Micron Deep-UV T-Shaped Gate Technology
Authors: Lai Yeong-Lin , Chang Edward Yi , Lee Di-Houng , Chen Szu-Hung
Published: March 2014

A class-B AlGaAs/InGaAs/GaAs pseudomorphic power high-electron-mobility transistor (HEMT) with high power performance has been developed. A simple fabrication method of a sub-micron T-shaped gate using the deep-UV lithography technology with tri-layer photoresists is presented for improvement of efficiency and gain of a pseudomorphic power HEMT. The AlGaAs/InGaAs/GaAs multinary compound material structure of the HEMT was grown by the molecular-beam epitaxy (MBE). The HEMT with a gate width of 3.36 mm and a gate length of 0.5 µm exhibits a transconductance of 383 mS/mm. The saturation drain-to-source current (IDSS) is 265 mA/mm. At an operation frequency of 1.9 GHz, the device demonstrates a power-added efficiency (PAE) of 65% at a drain bias of 1.2 V and a quiescent drain current of 30 mA (3.37% IDSS), The state-of-the-art power characteristics are, for the first time, achieved by the AlGaAs/InGaAs/GaAs pseudomorphic power HEMT using a sub-micron deep-UV T-shaped gate technology.
Resonant Tunneling Enhanced Electroluminescence in GaAs/(Al,Ga)As Asymmetric Coupled Double Quantum Well
Authors: Lu Chien-Rong , Hwang Fu-Kwan , Anderson James Robert
Published: March 2014

We have studied the low-temperature electroluminescence of a GaAs/AlGaAs asymmetric coupled double quantum well, and analyzed the temperature dependence and the external bias dependence of the light emission intensities. The third electron subband whose wavefunction is localized in the wide-well is nearly in resonance with the fourth electron subband whose wavefunction is localized in the narrow-well. When the narrow-well is biased positively with respect to the wide-well, the energy difference between the near resonant electron subbands is reduced, and the luminescence intensity increases due to the resonant tunneling enhancement. The temperature dependence analysis indicates that the major loss mechanism may be thermal activation of carriers out of the quantum wells followed by nonradiative recombination.
Interface and surface properties of ternary semiconductors
Authors: Scheer Roland
Published: March 2014

Recent results concerning surface and interface properties of Cu-chalcopyrite semiconductors are discussed. The aim of the paper is to improve the understanding of Cu-chalcopyrite systems. We treat surface structures and surface states. Experimental surface data of thin films and crystals are interpreted in terms of Fermi-level pinning. We estimate the energetic position of surface states based on a tight binding model. Surface defect structures are discussed and a model for their impact on growth properties is proposed. Estimations of charge neutrality levels are given. Experimental heterojunction band offsets are compared with model predictions. For several systems we find clear correspondence between modeled and measured band offsets. Attempts are made to explain differences which occur for specific heterocontacts.
Study the Al-oxide/GaAs Interface Characteristics by Spectral Response of GaAs Solar Cells
Authors: Lee Shih-Chang , Wen Tzu-Chi , Lee Wei-I
Published: March 2014

The Al-oxide formed by wet-thermal oxidation of AlAs is used as the anti-reflection (AR) coating of the GaAs solar cell. Results of spectral response measurement suggest that the interfacial recombination velocity is extremely high at the Al-oxide/GaAs interface. Adding a 20-nm-thick Al0.4Ga0.6As barrier layer between the Al-oxide and the GaAs emitter can reduce the influence of interfacial recombination and enhance the performance of the GaAs solar cell. The energy conversion efficiency of the GaAs solar cell utilizing the wet oxidation of AlAs to form the AR coating is 19.43% under the luminescence condition of one-sun, AM 1.5G and 100 mW/cm2.
XPS Study of CVT-grown CuAlSe2
Authors: Kuroishi Naotaka , Mochizuki Katsumi , Kimoto Kazuhiko , Arai Toshihiro
Published: March 2014

CuAlSe2 crystals grown by CVT(Chemical Vapor Transport) method were supplied to the surface analysis of XPS in detail. Chemical shift of Cu due to Cu-O and Cu-Se bonds was clearly observed It was known that oxidation starts after growth and the degree depends on the growth condition of the target crystal. Al is lacking near surface region due to its high reactivity Copper and selenium are stable and distribute almost uniformly.
X-Ray Photoelectron Spectroscopic Studies of Some Ternary Magnetic Chalcogenide Semiconductors
Authors: Tsurkan Vladimir , Demeter Mihaela , Plogmann Stefan , Neumann Manfred
Published: March 2014

X-ray photoelectron spectroscopic investigations of some ternary magnetic semiconductor chalcogenides ACr2X4 (A=Cu, Cd, Hg, Fe, Mn, Zn; X=S, Se) were performed. From the observed splitting of the 3s core levels of the Cr, Fe and Mn ions, the configurations of these ions were determined to be 3d3, 3d6 and 3d5 respectively. The splitting of the Cr- 2p core levels in the investigated crystals was also observed.
Role of Defects and Defect Metastabilities for the Performance and Stability of Cu(In,Ga)Se2 Based Solar Cells
Authors: Rau Uwe
Published: March 2014

This article deals with two important aspects of the defect physics and defect chemistry in Cu(In,Ga)Se2 polycrystalline thin films. First, metastable defects in Cu(In,Ga)Se2 lead to persistent changes of the electrical properties of the bulk material upon illumination. The article discusses a light induced defect reaction as the microscopic origin of the observed electrical behavior. The second part compares recent models for the surface of polycrystalline Cu(In,Ga)Se2 and their consequences for the formation of the ZnO/CdS/Cu(In,Ga)Se2 heterojunction.
Difference in Mechanism of Compensation by Cu Vacancies between n-Type Zn- and Cd-Doped CuInS2 Crystals
Authors: Yamamoto Tetsuya , Luck Ilka V. , Scheer Roland , Katayama-Yoshlda Hiroshi
Published: March 2014

The total energy calculations for Zn-doped CuInS2 crystals (CuInS2:Zn) show that the formation of a Cu vacancy (VCu) whose site is 5.52 Å away from the Zn (Cu-substitution species) sites is energetically favorable. In other words, the Zn-donor states in CuInS2:Zn are easily compensated by the VCu generated by the Zn doping. On the other hand, for CuInS2:Cd, where the strong chemical bonds of Cd-S atoms are formed, we find more distant VCu from the Cd sites. In addition, we find delocalized Cd-donor states for CuInS2:Cd compared with those for CuInS2:Zn. From the above findings, we predict that the Cd species can be considered as suitable candidates for use as donor dopants. We also discuss the diffusion properties of Zn or Cd via the VCu in CuInS2 crystals for the materials design for the fabrication of a buried-homo junction in CuInS2-based solar cells.
Non-Stoichiometry and Defect Structure of CuInSe2
Authors: Rogacheva Elena , Tavrina Tat'yana , Gladkikh Liliya
Published: March 2014

The precise determination of unit cell parameters of polycrystalline Cu1-y
In1+y
Se2 alloys with variable cation ratio ([Cu]/[In] = 1.01-0.90) and fixed Se content (50.0 at.%) and Cu1-zIn1-zSe2(1+z) alloys under Se deficit and excess relative to the stoichiometric composition and fixed cation ratio ([Cu]/[In] = 1.0) was performed. The conclusions about the predominant types of defects were made. Increase in lattice parameters under deviation from stoichiometry in the Cu1-y
In1+y
Se2 alloys to the In excess side is attributed to the appearance of substitution defects InCu. A minimum at z ∼ 0.01 (∼ 50.5 at.% Se) in the concentration dependences of unit cell parameters of the Cu1-zIn1-zSe2(1+z) alloys is explained by the change in the defect formation mechanism in the vicinity of this composition caused by defect interactions. The growth in unit cell parameters observed under Cu excess in the Cu1-y
In1+y
Se2 alloys and under Se deficit in the Cu1-zIn1+zSe2(1+z) alloys is attributed to the formation of Cu interstitial atoms.
New Perspectives of Defect Physics and Defect Chemistry for Copper Ternary Chalcopyrite Semiconductors
Authors: Chang Hsueh-Hsin , Ueng Herng-Yih , Zhong Tang-Xuan , Hwang Huey-Liang
Published: March 2014

An integrated scheme of defect physics and defect chemistry was developed to study the electronic and electrical properties of CuInSe2. We found that the Madelung energy and relaxation process play significant roles in the defect physics formulation, and some computed data of defect concentrations and the corresponding carrier concentrations using our new scheme are presented.
Ternary Compounds A2B4C2
5 and A1B3C2
6: Frenkel Defects Concentration
Authors: Voevodin Valery , Voevodina Olga
Published: March 2014

Ternary compounds ZnGeP2, CdGeAs2, AgGaS2, AgGaSe2 are under consideration. In the framework of the Weiser's model thermodynamical parameters of the intrinsic interstitials and their concentrations as a function of liquidus temperatures are estimated.
Electron Spin Resonance Studies of Fe in CuGaSe2
Authors: Sato Katsuaki , Katsumata Yuji , Nishi Takao
Published: March 2014

ESR spectra (X band) were measured in single crystals of CuGaSe2 prepared by traveling heater method (THM) and iodine transport (IT) technique. In the THM-crystal an anisotropic signal around 200-300 mT, which is completely quenched by H2-annealing, is assigned to Fe3+. On the other hand, two types of ESR spectra were observed in IT-crystals. In the type-1 spectrum, nearly isotropic lines were found at 110-130, 400 and 890-950 mT. The spectral features are similar to that of Fe3+ in CuInSe2. On the contrary, in the type-2 spectrum, strongly anisotropic resonance lines were observed and were assigned to Fe2+ states. Annealing in Se vapor completely quenches the type-2 signal but results in appearance of the type-1 spectrum. This finding may be explained by an assumption that the Fermi level is lowered below the Fe2+/Fe3+ demarcation level by reduction of Se-vacancy brought about by the Se- vapor anneal.
The Nuclear Magnetic Resonance of Heusler Compounds Fe2+xV1-xAl
Authors: Ooiwa Kiyoshi
Published: March 2014

Nuclear magnetic resonance(NMR) experiments were performed for 51V and 27A1 in Fe2+x
V1-x
Al (-0.10≦x≦ 0.10). NMR spectra of 51V and 27A1 were observed. The Knight shifts of 51V and 27A1 are +0.6% and +0.0%, respectively. The shifts of 51V and 27A1 are almost independent of temperature. The line widths depend on temperature and composition through magnetic susceptibility. This shows that there exists randomly distributed magnetic moments. The relaxation rates increase rapidly above room temperature which suggests the existence of an energy gap of 0.5eV.
Crystal Growth of Cu-III-Ge-Se4 Quaternary Compounds (III=Ga, In) by vertical Bridgman methods
Authors: Maeda Takashi , Matsushita Hiroaki , Katsui Akinori
Published: March 2014

Single crystals growth of Cu-III-Ge-Se4 quaternary compounds (III = Ga, In) has been investigated by the vertical Bridgman method. It was found that in order to crystallize CuInGeSe4 single phase, the excess-selenium concentration x above 0.5 was needed when the starting composition is expressed by CuInGeSe4+x. Furthermore, it was shown that the crystals with compositionally uniform distribution along the growth direction was obtained by the lowing rate of ampoule above 0.7 cm/h/.
Long and Short Range Ordering of CuInSe2
Authors: Chang Chih-Hung , Wei Su-Huai , Johnson Wayne , Bhattacharya Raghu , Stanbery Billy , Anderson Tim , Duran Randy
Published: March 2014

Cu K-edge X-ray Absorption Fine Structure (XAFS) measurements were performed on CuInSe2 samples with different compositions near the AIBIIIC2
VI stoichiometry and CuIn5Se8. The Cu-Se bond length was determined to be independent of the Cu content. This result is consistent with first-principle total energy calculations for this system.
Stabilization of Manufacturing Process of CIGS Solar Cell with Treatment of CIGS Surface by In and S Containing Solution
Authors: Hashimoto Y. , Nishiwaki S. , Negami T. , Wada T.
Published: March 2014

CuInSe2 (CIS) single crystal was treated in a solution containing 0.005M InCl3 and 0.1M thioacetamide. Transmission electron microscopy with micro region chemical composition analyses and electron diffraction analyses of the cross-sectional CuInSe2 single crystal revealed the formation of a CuInS2 layer on the CuInSe2 single crystal. Cu(In,Ga)Se2 (CIGS) solar cells applied the surface modification showed little dispersion of cell performance and solar cells with high performance were obtained reproducibly.
Structural Aspects of Band Gap Grading in Cu(In,Ga)(S,Se)2-Based Solar Cells
Authors: Kötschau I. M. , Dullweber T. , Kerber H. , Wiesner H. , Magorian-Friedlmeier T. , Rau U. , Schock H.-W.
Published: March 2014

Structural analysis of multinary Cu(In,Ga)(S,Se)2 films demonstrates the feasibility of compositional grading in the depth of the absorber with respect to the S/(S+Se) ratio. Solar cells prepared from films with moderate S/Se gradients exhibit high open circuit voltages and efficiencies up to 13.9%. In this contribution we investigate strong S/Se gradients. Of particular interest are the thickness of a nearly homogeneous top layer as well as the impact of the crystallinity on the current voltage characteristics of solar cells. We show that the crystallinity of a homogeneous top layer strongly correlates with the performance of the corresponding devices.
Solar cell using a highly structured pin-junction and CuInS2 as an extremely thin absorber
Authors: Kaiser I. , Ernst K. , Fischer Ch.-H. , Lux-Steiner M. Ch. , Könenkamp R.
Published: March 2014

A new cell design using CuInS2 (CIS) as an extremely thin absorber (ETA-solar cell) is explored. The new cell allows the collection of photogenerated charge carriers over short transport distances. The charge separation is field-assisted and hence the diffusion length is of less importance for ETA-cells. It is shown in this paper that the properties of the (CIS)layer strongly depend on the porosity of the substrate. From transmission and reflection measurements we find that scattering of light within the porous structure results in high light absorption. Photoluminescence spectra indicate, that states in the band gap of CIS depend on the porosity of the structure. The short circuit current density of the complete ETA solar cell shows a maximum with increasing thickness of the absorbing layer.
A Low-Cost Approach to Fabrication of Multinary Compounds for Energy-Related Applications
Authors: Bhattacharya Raghu N. , Deb Satyen K.
Published: March 2014

Non-vacuum electrodeposition and electroless deposition techniques with a potential to prepare large-area uniform precursor films using low-cost source materials and low-cost capital equipment are very attractive for the growth of compound materials for superconductors and photovoltaic applications. In the first part, a low-cost electrodeposition (ED) method will be discussed for fabrication of high-temperature Tl-oxide-based superconductors. In the second part, electrodeposition and electroless deposition of semiconductor Cu-In-Ga-Se thin films will be discussed.
Deep Levels and Space Charge Distribution in Cu(In,Ga)Se2 Photovoltaic Devices
Authors: Igalson Małgorzata , Stolt Lars
Published: March 2014

ZnO/CdS/Cu(In,Ga)Se2 photovoltaic devices have been investigated at low temperatures after the samples have been subjected to various forward and reverse biases or illumination at room temperature and during cool-down. The C-V characteristics has been measured and interpreted as distorted by a charge captured in more than 2-1022 m-3 of deep traps. Subsequent illumination by use of red and blue light reveals very high concentration of midgap centers in the 10-20 nm layer of absorber close to the heterointerface. Their presence might be a source of efficiency losses previously attributed to the defects in CdS.
Lasing Possibility in Rare-earth Element Doped Thiogallate Compounds
Authors: Iida Seishi , Matsumoto-AoKi Tamao , Morita Tomomi , Mamedov Nazim , Tagiev Bakhadur G. , Gashimzade Firudin M. , Sato Katsuaki
Published: March 2014

In this paper discussions based on the result of a pump-probe experiment are given on a possibility of application of the emission from Ce doped CaGa2S4 to production of a new laser. Existence of enough gain for laser action was clearly demonstrated from the analysis of the experimental result. Using the phonon-terminated character of this emission, construction of an unique laser having wide wavelength tunability covering violet to green region is thought to be possible. As far as optically pumped lasers are concerned, the only problem to be solved is to grow good single crystals having a suitable size (1×1×1 mm3 or more). In order to realize injection type semiconductor lasers with this material, we have to study conduction type and conductivity control technique together with a suitable epitaxial growth method for obtaining thin films of this material. It is pointed out that Ce doped SrGa2S4 and BaGa2S4 are also strong candidates for construction of similar lasers.
Optical and electrical properties of impurity doped Pbi1-xCaxSi1-ySey thin films prepared by hot wall epitaxy
Authors: Abe Seishi , Masumoto Katashi
Published: March 2014

We have investigated the optical and the electrical properties of impurity doped Pb1-x
Ca
x
S1-y
Se
y
thin films. The high carrier concentration was obtained by doping with Bi as a n-type or Tl as a p-type impurity for cladding layers in a laser diode. The infrared absorption of the Bi doped films was observed on the transmission spectra. The relation between the absorption coefficient α and the carrier concentration n was expressed as α=3.24×10-12
n
0.78 at 10 µm, and it is required to control the carrier concentration appropriately for low absorption loss in the cladding layers.
Blue Photoluminescence and Resonant Raman Scattering in Bulk CuAlSe2 Grown by THM
Authors: Shim Yonggu , Kimura Hiroaki , Horikawa Syuichi , Yamamoto Nobuyuki
Published: March 2014

Blue band edge photoluminescence is observed for the first time in CuAlSe2 single crystals grown by THM from the 5% Cu2Se-rich polycrystalline raw materials. Exciting light energy dependence of the photo-luminescence and resonant Raman scattering exhibits a strong enhancement at 2.601 eV, close to the energy of a bound exciton. A model of the radiative recombination responsible for the newly observed emissions is proposed with a deep donor and a deep acceptor with unclarified origin yet. The value of a small band gap reduction, estimated from the energy shift in the luminescence spectrum, is found to be consistent with that of the In-alloying effect on band gap in the THM-grown CuAlSe2.
Characteristics of the AlGaAs/GaAs Broad-Area Vertical-Cavity Surface-Emitting Lasers
Authors: Yang Hung-Pin D. , Su Yeung-Sy , Jiang Wen-Jang , Wang Mei-Li , Tsou Yi-Jen
Published: March 2014

We report the results of the AlGaAs/GaAs broad-area vertical-cavity surface-emitting lasers at 850 nm. A maximum laser optical power of 23.4 mW was measured for a device with a 50-µm aperture. The near-field characteristics and spectrum of the devices were also measured and analyzed.
Modulation Frequency Dependences of Photoacoustic Signal Intensity and Phase for CdInGaS4
Authors: Shen Qing , Toyoda Taro
Published: March 2014

Modulation frequency dependences of photoacoustic (PA) signal intensity and phase in a transmission geometry were experimentally measured and theoretically calculated for CdInGaS4 It was shown that the PA signal originated from both the electronic transport process and the heat diffusion process in the sample, which could be separated at a characteristic frequency fmin. It was found that the PA signal phase reversed and the PA signal intensity showed a minimum at the frequency fmin.
Growth of Twin-Free AgGaS2 Single Crystals by a Self-Seeding Vertical Gradient Freezing Method and Difference Frequency Generation Using These Crystals
Authors: Niwa Eiji , Haidar Sajjad , Masumoto Katashi , Ito Hiromasa
Published: March 2014

We investigated different conditions for the growth of twin-free crystals of AgGaS2 and then examined difference frequency generation (DFG) using the crystals to apply the new technology to coherent light sources tunable from 5 to 12µm. The number of lamellar twins in a crystal decreased with increasing growth rate and vanished at growth rates greater than or equal to about 1 mm/hour. Growth under these conditions allowed us to obtain the twin-free AgGaS2 single crystals. Using these crystals, a DFG output of 5-12µm was obtained by angle tuning on phase matching angle ranges of 32-37° for type-I and 38-43° for type-II respectively. These phase-matching angles coincided with angles of the growth directions from the c-axis. It was found that longer optical crystals capable of producing difference frequency waves tunable from 5 to 12µm could be prepared from the AgGaS2 single crystal boules grown by our VGF method, without suffering cutting losses.