New forms of In<Subscript>2</Subscript>Se<Subscript>3</Subscript> and Ga<Subscript>2</Subscript>Se<Subscript>3</Subscript> prepared by reacting InAs and GaAs substrates with selenium

Ga₂Se₃ and In₂Se₃ prepared through heterovalent substitution during thermal annealing of single-crystal gallium arsenide and indium arsenide substrates in selenium vapor in a quasi-closed system have been characterized by electron diffraction, scanning electron microscopy, and X-ray microanalysis. Cubic phases of In₂Se₃ (a ₀ = 1.1243 nm and a ₀ = 1.6890 nm) and Ga₂Se₃ (a ₀ = 1.0893 nm and a ₀ = 1.6293 nm) have been identified for the first time.     

X-ray-induced conductivity in gallium sesqui-selenide

The X-ray-induced dc conductivity of gallium sesqui-selenide (Ga₂Se₃) crystals characterized by anomalously high radiation resistance was studied as a function of the intensity of incident radiation. The obtained results show that Ga₂Se₃ crystals can be used as working elements of detectors for X-ray dosimetry in the range of radiation intensities studied.     

Chemical Interaction of Indium Arsenide and Gallium Antimonide with Sulfur

The reactions of fine-particle indium arsenide and gallium antimonide with sulfur and the composition of the reaction products obtained from different starting mixtures were studied by differential thermal analysis, x-ray diffraction, chemical analysis, and IR spectroscopy. The reaction between indium arsenide and sulfur begins at lower temperatures in comparison with gallium antimonide, is autocatalyzed, and yields In₂S₃ and As₂S₃. The reaction between gallium antimonide and sulfur yields Ga₂S₃, Sb₂S₃, and (GaS)₂. Thermolysis of the resultant sulfide mixtures ensures a more complete separation of the sulfides in the case of indium arsenide.     

Preparation of AgIn1−xGaxSe2 films from sol–gel derived precursors via a coating method

AgIn_1?xGa_xSe₂ films were prepared via coating the pastes that contained sol–gel derived precursors and selenium powders, followed by the normal heating process without using H₂Se. Pure-phased AgIn_1?xGa_xSe₂ films were successfully obtained after heating in a reducing atmosphere (H₂/N₂) at 500 °C for 0.5 h. As the flow rate of the carrier gas was reduced, In₂O₃ and Ag₂Se phases in the obtained films disappeared owing to prolonged residence time for selenium vapor to react with the precursors. In the paste-coating process, the gallium-ion content of the prepared films was effectively adjusted using the sol–gel route. The lattice constants of AgIn_1?xGa_xSe₂ decreased with increasing the gallium-ion contents. The uniformity throughout AgIn_1?xGa_xSe₂ films was confirmed by using the grazing incident X-ray diffraction analysis. The band gap energy increased nonlinearly from 1.27 to 1.63 eV as the molar ratio of gallium ions to IIIA ions (indium ions and gallium ions) increased from 0.2 to 0.8.     

Heat treatment effect on the structural and optical properties of Ga2Se3-Ga2S3 thin films

The structural properties of the 50 mol% Ga₂Se₃-50 mol% Ga₂S₃ system in thin-film form were studied using an X-ray diffraction technique. As-deposited films had an amorphous nature, whereas films heat treated for 2 h at 400 °C in a vacuum of 10^–2 Pa had a single-phase (cubic) polycrystalline nature with lattice constanta=0.532 nm. The optical properties of Ga₂Se₃-Ga₂S₃ thin films as-deposited and as-heat treated were also studied. It was found that heat treatment strongly affects the optical constants as well as the energy gap, which can be attributed to compositional as well as structural changes.     

Ag2SeGa2Se3 pseudobinary phase diagram

The pseudobinary Ag₂Se-Ga₂Se₃ phase diagram has been redetermined by differential thermal analysis, x-ray diffraction, and crystal growth studies. A new ternary phase, Ag₉GaSe₆, has been observed, and the phase boundaries of the solid solutions based on AgGaSe₂ and Ga₂Se₃ have been measured. The optical scattering observed in slow-cooled crystals of AgGaSe₂ is due to precipitates of a Ga₂Se₃-based solid solution, which has the approximate composition AgGa₇Se₁₁. The new Ag₂Se-Ga₂Se₃ diagram differs significantly from the one given by Palatnik and Belova but is qualitatively similar to the Ag₂S-Ga₂S₃ diagram recently reported by Brandt and Krämer.     

Heat Capacity and Thermodynamic Functions of Ga<Subscript>2</Subscript>Se<Subscript>3</Subscript> from 14 to 320 K

The heat capacity of Ga₂Se₃ is measured from 14 to 320 K by adiabatic calorimetry. The smoothed heat capacity data are used to evaluate temperature-dependent thermodynamic functions (entropy, enthalpy increment, and reduced Gibbs energy) of gallium selenide. Under standard conditions, the thermodynamic properties of Ga₂Se₃ are C _p ⁰ (298.15 K) = 120.8 ± 0.2 J/(K mol), S⁰(298.15 K) = 180.4 ± 0.4 J/(K mol), H⁰(298.15 K) - H⁰(0) = 25.32 ± 0.05 kJ/mol, and Φ⁰(298.15 K) = 95.52 ± 0.19 J/(K mol). The Debye characteristic temperature of Ga₂Se₃ evaluated from heat capacity data is 340 ± 10 K.     

Thermal oxidation of amorphous GaSe thin films

In this work the results of the thermal oxidation of GaSe thin films in air at different temperatures are presented. The structural and morphological characteristics of the thermally annealed products were studied by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The as-deposited GaSe films were amorphous and they transformed into polycrystalline GaSe films with a hexagonal crystal structure at a temperature around 400 °C. Thermal oxidation at 650 °C resulted in the formation of mixed Ga₂Se₃ and Ga₂O₃ compounds both in the monoclinic phase. At higher temperatures, Ga₂Se₃ disappeared and complete oxidation of the initial compound occurred. The optical energy gaps of products were determined at room temperature by transmittance measurements using UV–vis–NIR spectroscopy.     

Systeme Ga2S3FeS — Diagramme de phase — etude cristallographique

The system was studied by DTA, X-ray diffraction and in particular by the Guinier-Lenné method. Eight intermediate phases are described. 1) Three solid solutions in the Ga₂S₃ region : a) a wurtzite-type solid solution (T > 1000° C ; 0.05 < n < 0.23) (n = Fe $\text{at}\text{Fe}$ at+Ga at), b) a blende-type solid solution (700°C < T < 980°C ; 0.10 < n < 0.20) with many stacking faults, c) a non-stoichiometric hexagonal phase α'Ga₂S₃ type (T < 700°C, 0.07 < n < 0.12). 2) for n = 0.20 and T = 540°C a superstructure of orthorhombic wurtzite-like array FeGa₄S₇. 3) From n = 0.20 through n = 0.27, a non stoichiometric superstructure of tetragonal-like array has the CdGa₂S₄ type (600°C < T < 1030°C). 4) For n = 0.33, the FeGa₂S₄ has two forms depending from the temperature : a) a low temperature form is trigonal ; b) a high temperature form is orthorhombic type ZnAl₂S₄. Transition temperature is 1010°C. 5) For n = 0.50, Fe₂Ga₂S₅ polytypes : a) Fe₂Ga₂S₅α 1T type Mn₂Ga₂S₅ ; b) Fe₂Ga₂S₅ 2H ; c) Fe₂Ga₂S₅ 3R type Mn₂Al₂Se₅. A phase diagram is proposed.     

Preparation et structure de Ga2S3α type wurtzite lacunaire

Preparations of powdered and crystalline αGa₂S₃ are described. Structure of αGa₂S₃ is established from single crystal determination (R = 0.058). These is a superstructure of wurtzite type, with ordered vacancies on gallium positions. A polymorphism of Ga₂S₃ is described.     

X-ray study of the air-oxidiseda-Ga2Se3 and Ga2Te3 powders

X-ray studies of the stoichiometrically prepareda-Ga₂Se₃ and Ga₂Te₃ are reported after various stages of air-oxidation in the temperature ranges 250 to 825° C and 250 to 650° C respectively. Diffractometric powder data of Ga₂Te₃ are also reported over the complete 2ϑ range with remarkable difference in the relative intensities of the (444) and (642) reflections. Ina-Ga₂Se₃ the oxidation proceeds by formation of the most stable phase, beta-gallium sesquioxide, complete oxidation occurring at 650° C. For Ga₂Te₃ a mixture of Ga₂TeO₆ and TeO₂ is obtained as the intermediate oxidation products in the range 500 to 600° C, while at 450° C some extra lines which could be indexed on the super-lattice cell of Ga₂Te₃, along with Te and unchanged Ga₂Te₃ lines, are observed. Oxidation at the higher temperature of 650° C led to the disappearance of TeO₂ lines leaving Ga₂TeO₆ as the final well-crystallised phase.     

Vacancy ordering and lithium insertion in III2VI3 nanowires

Superlattice structures resulting from vacancy ordering have been observed in many materials. Here we report vacancy ordering behavior in III₂VI₃ nanowires. The formation of layer-like structural vacancies has been achieved during the synthesis of In₂Se₃ nanowires through a vapor-transport route. Doping In₂Se₃ nanowires with small amounts of Ga during synthesis can completely change the structural vacancy ordering from a layer-like to a screw-like pattern for (In _x Ga_1−x )₂Se₃ nanowires. Lithium atoms can fill in the layer-like structural vacancies of In₂Se₃ nanowires and generate new types of vacancy and lithium atom ordering superlattices. The screw-patterned vacancies of (In _x Ga_1−x )₂Se₃ nanowires show reversible lithium insertion. Our results contribute to the understanding of structure property correlations of III₂VI₃ materials used in lithium ion storage, photovoltaics, and phase change memory.     

Synthesis and characterization of morphologically different high purity gallium oxide nanopowders

High purity gallium oxide nanopowders have been synthesized by using a simple precipitation technique with calcination at elevated temperature. From the X-ray pattern, the phase purity of the synthesized powders was confirmed as β-Ga₂O_3. Elemental quantification (stoichiometry) of Ga₂O₃ was also examined from the X-ray energy dispersive analysis (EDAX). Based on the recorded Fourier Transform Infrared (FTIR) spectrum of Ga₂O_3, the IR bands due to Ga–O bond and crystal lattice vibrations have been identified in the wavenumber range 400–4,000 cm⁻¹. From the measured SEM images, it is obvious to notice that the pH value has been playing a dominant role in obtaining morphologically different gallium oxide nanopowders. Thermogravimetric analysis reveals 8.3% of weight loss when the sample was heated to the temperature of 1,100 °C from the room temperature, which also shows a crystalline phase transformation. It is very interesting to report that a broad blue emission at 455 nm has been measured from the synthesized gallium oxide nanopowders.     

Phase investigations in the silver-gallium-sulphur system

The binary join Ag₂SGa₂S₃ and some supplementary compositions in the ternary system AgGaS were examined by differential thermal analysis and X-ray diffraction. From the experimental results the phase diagram of the Ag₂SGa₂S₃ system was constructed. Besides the well-known chalcopyrite analog AgGaS₂ two additional compounds of composition Ag₉GaS₆ and Ag₂Ga₂₀S²₃₁ were established, both being dimorphic. Outside the binary section only one new phase, a Ag-containing rhombohedral modification of gallium sulphide, GaS:Ag(3R), could be found. Crystal data for all phases investigated are given. Ag₉GaS₆ is a representative of a group of possible superionic conductors with icosahedral structure.     

Effect of gallium on the electrical properties and photoresponse of CuIn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>2</Subscript> films

Semiconducting films of CuIn_{1 − x} Ga _x Se₂ solid solutions have been produced on CdS by selenizing metallic layers in flowing nitrogen. We have optimized the film growth conditions and investigated the structure, electrical properties, energy band structure, and photoconversion quantum efficiency of the films. With increasing gallium content, the band gap of the CuIn_{1 − x} Ga _x Se₂ (x = 0, 0.2, 0.25, 0.30) films increases, reaching 1.27 eV. The films are potentially attractive for use in high-efficiency solar cells.     

Transport properties of TlIn1−x Ga x Se2 (0 ≤ x ≤ 0.3) crystals

Single crystals of TlIn_1?x Ga _x Se₂ solid solutions have been grown by the Bridgman-Stockbarger method. As shown by x-ray diffraction, the solid solutions crystallize in tetragonal symmetry, and their lattice parameters decrease with decreasing average atomic weight. The electrical conductivity and Hall coefficient of the solid solutions have been measured as functions of temperature, and their principal semiconductor parameters have been determined. Pseudopotential band-structure calculations have been used to analyze the origins of the valence and conduction bands in the parent compound TlInSe₂. The results indicate that the increase in the band gap of the TlIn_1?x Ga _x Se₂ solid solutions upon partial gallium substitution for indium in TlInSe₂ is due to the shift of its valence band to lower energies.     

Powder X-ray diffraction identification of some new phases in the Na2SAl2S3 system

Four new phases in the Na₂SAl₂S₃ system have been identified by powder X-ray diffraction analysis. All four phases have Na₂S:Al₂S₃ ratios greater than 1:1. Analysis with X-ray diffraction and energy dispersive spectroscopy with a scanning electron microscope indicated provisional stoichiometries of α-Na₃AlS₃, β-Na₃AlS₃, and Na₅AlS₄ for three of the new phases. The fourth phase has yet to be identified.     

Degradation and Fracture of Crystals of Gallium and Indium Selenides

In the Laue patterns of crystals of gallium selenide, we experimentally established the blurring of diffraction spots in the radial direction (asterism). The elongation of tails depends on the number, shape, and dimensions of fragments. The isomorphic substitution of elements results in the appearance of Ga _x In_1 – x Se and (In_0.6Ga_0.4)₂Se₃ solid solutions. In the course of deformation and fracture of mixed (In_0.6Ga_0.4)₂Se₃ crystals, slip bands reach the surface due to mechanical stresses. The spalling of crystals occurs at an angle about 45° to the direction of applied tensile stresses. Brittle fracture of the alloy is accompanied by the simultaneous disintegration of a crystal at several sites.     

Influence of Ga content on defects in CuInxGa1 − xSe2 based solar cell absorbers investigated by sub gap modulated photocurrent and admittance spectroscopy

In this work, we investigate the influence of gallium content on the defects properties of co-evaporated CuIn_xGa_1 − xSe₂ by sub gap modulated photocurrent spectroscopy and admittance spectroscopy techniques. A series of CuIn_xGa_1 − xSe₂ based solar cells with different gallium content in the range from 0% to 33%, and with the same CdS buffer layer have been investigated. On one hand, photocurrent spectroscopy results show 2 types of defects named D1 and D2, and on the other hand, admittance spectroscopy results exhibit only one type of defect. I-V curves show that one of the two defects probed by photocurrent is responsible of the dominant recombination mechanisms next to the heterointerface, between the absorber and the buffer layers. Moreover, I-V curves under AM 1.5 conditions show that the cell with no probed D2 defect presents the best photovoltaic performances.     

Effect of the composition and annealing conditions of precursor films on the structure of thin CuIn1 − x GaxSe2 (0 ≤ x ≤ 0.7) layers

A technique has been developed for the preparation of CuIn _x Ga_{1 ? x} Se₂ layers through closed-space selenization of precursor films containing intermetallic compounds. We also have produced CuIn _x Ga_{1 ? x} Se₂ films by selenizing metallic precursor films. Examination of the CuIn _x Ga_{1 ? x} Se₂ layers by X-ray diffraction, atomic force microscopy, and scanning electron microscopy has shown that the use of inter-metallic precursors offers a number of important advantages: phase purity and homogeneity of CuIn _x Ga_{1 ? x} Se₂ layers, in combination with good adhesion of the layers to substrates (glass or glass/molybdenum).