Effect of impurity (Te and Zn) incorporation in the density of defect states in thin films of Se90In10 and Se75In25 glassy alloys

In this paper we report the effect of Te and Zn incorporation on the density of defect states of two binary Se–In glassy systems. For this purpose, we have chosen here two well known Se₉₀In₁₀ and Se₇₅In₂₅ binary glassy alloys. Thin films of Se₉₀In₁₀, Se₇₅In₂₅, Se₇₅In₁₀Te₁₅ and Se₇₅In₁₀Zn₁₅ glassy alloys prepared by quenching method, were deposited on glass substrate using thermal evaporation technique. Current–voltage characteristics have been measured at various fixed temperatures in the thin films under study. Ohmic behavior was observed at low electric fields while at high electric fields current becomes superohmic. An analysis of the experimental data confirms the presence of space charge limited conduction in Se₉₀In₁₀, Se₇₅In₁₀Te₁₅ and Se₇₅In₁₀Zn₁₅ glassy alloys. It was found that the absence of space charge limited conduction in Se₇₅In₂₅ may be due to joule's heating at high fields. By applying the theory of space charge limited conduction, the density of defect states near Fermi level was calculated. The peculiar role of the additives (Te and Zn) in the pure binary Se₉₀In₁₀ and Se₇₅In₂₅ glassy alloys is also discussed in terms of electro-negativity difference between the elements involved.     

Nanolayer of the A2IIIB3VI (111) phase with ordered cation vacancies on GaAs(111) and InAs(111)

The surface of GaAs(111) and InAs(111) substrates has been investigated by transmission and scanning electron microscopy after thermal treatment in selenium vapor. A pseudomorphic growth of single-crystal phases of indium selenide In₂Se₃(111) and gallium selenide Ga₂Se₃(111) is found; these compounds are crystallized into a sphalerite lattice with ordered stoichiometric cation vacancies. A model of an atomic surface is proposed for the In₂Se₃(111) and Ga₂Se₃(111) structures. The reconstruction of the (√3 × √3)-R30° surface of GaAs(111) and InAs(111) after treatment in Se vapor is considered within this model.     

Chemical shifts of the K-absorption discontinuities of germanium and selenium in some amorphous systems

In the present investigation the chemical shifts of the K-absorption discontinuities of germanium and selenium have been studied in their amorphous chemical compounds Ge₁₀Se₉₀, Ge₃₀Se₇₀, Ge₁₀Se₈₀Te₁₀ and Ge_33.3Se₄₀Te_26.7 using a 1 m Cauchois type bent crystal (mica) X-ray spectrograph. A graph of the chemical shift ΔE in binary compounds against the effective charge q on the absorbing atoms has been plotted. This plot is helpful in determining the effective charges in ternary compounds in which they cannot be calculated theoretically.     

Interface reconstruction in the Ga<Subscript>2</Subscript>Se<Subscript>3</Subscript>/GaAs(100) and In<Subscript>2</Subscript>Se<Subscript>3</Subscript>/InAs(100) nanoheterostructures

The surface of GaAs(100) and InAs(100) substrates thermally treated in selenium vapor has been investigated by transmission electron microscopy (TEM) and reflection high-energy electron diffraction. Transmission electron microscopy and high-energy electron diffraction data on these heterostructures confirms the epitaxial pseudomorphic growth of the gallium selenide Ga₂Se₃(100) and indium selenide In₂Se₃(100) phases with ordered stoichiometric cation vacancies. A model of the atomic structure of the Ga₂Se₃(100) and In₂Se₃(100) surfaces is proposed, and the 2 × 2 reconstruction of the GaAs(100) and InAs(100) surfaces after treatment in selenium vapor is discussed within this model.     

Application of diffusion couple technique for the determination of the Ti‐Bi‐Sn phase diagram

The system Ti‐Bi‐Sn has been investigated by solid/liquid diffusion couples at 500, 600, 700 and 800°C. A non‐negligible solubility of Sn into solid Bi is found. Diffusion layers of the recently revealed ternary compound Ti₃BiSn have been observed, thus its existence has been confirmed. Data about the homogeneity ranges of the binary end‐system compounds have been obtained. The assessed growth constants of the diffusion layers are comprised in the interval 10^‐12 –10^‐14 m².s^‐1. The phases participating in the hypothetical ternary eutectic reaction, probably are: (Bi), (Sn), Liquid and Ti₂Sn₃. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Properties of AgGa1‐xInxSe2 single crystals grown by Bridgman method

High‐pure and single‐phase AgGa_1‐xIn_xSe₂ (x=0.2) polycrystalline was synthesized by the mechanical and temperature oscillation method. Adopting the modified Bridgman method an integral AgGa_1‐xIn_xSe₂ single crystal with diameter of 14 mm and length of 35 mm has been obtained at the rate of 6 mm/day. It was found that there is a new cleavage face which was (101), and observed the four order X‐ray spectrum of the {101} faces. By the method of DSC analysis the melting and freezing points of the AgGa_1‐xIn_xSe₂ (x=0.2) single crystal were about 828°C and 790°C. The transmission spectra of the AgGa_1‐xIn_xSe₂ (x=0.2) sample of 5×6×2 mm³ were obtained by means of UV and IR spectrophotometer. The limiting frequency was 774.316nm and the band gap was 1.6eV. It can be found in the infrared spectrum that the infrared transmission was above 60% from 4000cm^‐1 to 600cm^‐1. The value of α in 5.3µm and 10.6µm were 0.022cm^‐1 and 0.1cm^‐1 respectively. All results showed that the crystal was of good quality. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermoelectric Behaviour of Some Phases in the In?Se System

The differential e.m.f. of In₆Se₇ single crystals as a function of temperature have been measured. The electron to hole mobility ratio is determined to be μ_n/μ_p = 3.62. The effective masses of electrons and holes are 4.21 × 10⁻³³ kg and 9.01 × 10⁻²⁹ kg, respectively. The diffusion coefficient for holes and electrons as well as the diffusion length of free charge carriers have been determined.     

Crystallization kinetics and optical band gap studies of Se96In4 glass before and after slow neutron irradiation

Results of differential scanning calorimetry (DSC) under non-isothermal condition on Se₉₆In₄ semiconducting chalcogenide glass before and after slow neutron irradiation, for different exposure times, have been reported and discussed. Some of Sn atoms have been injected into the glass by nuclear transmutation processes and the binary glass is converted into a ternary. This is accompanied by an increase in the activation energy of crystallization, E_c, and in the glass transition temperature, T_g and a decrease in the glass transition activation energy, E_t, in the onset crystallization temperature, T_c and in the peak temperature of crystallization T_p. Optical band gap measurements have also been carried out, before and after irradiation, on identical thin pellets of Se₉₆In₄ glass. The energy band gap, E_g, is found to decrease upon irradiation. These effects have been attributed to a structural change upon doping and to irradiation induced defects.     

Contribution to the Ti‐Bi phase diagram

The system Ti‐Bi has been investigated by solid/liquid diffusion couples at 400, 500, 600 and 700 °C. Indication that the growth rate of the diffusion layers at 500 °C is linear has been found, with a growth constant of around 5 × 10^–11 m.s^–1. The existence of the Ti₂Bi phase has been confirmed. Some formerly unknown binary phases (TiBi, Ti₂Bi₃, TiBi₂) have been observed. The phase TiBi is, probably, identical with Ti₈Bi₉ reported previously. All intermediate phases suffer air corrosion, but in various degrees. A tentative variant of the Ti‐Bi phase diagram, including the newly found compounds, has been constructed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth improvement and characterization of AgGaxIn1−xSe2 chalcopyrite crystals using the horizontal Bridgman technique

AgGa_xIn_1?xSe₂ single crystals with x=0.4 have been grown by the horizontal Bridgman technique for nonlinear optical application requires phase matching. High purity polycrystalline synthesis of AgGa_xIn_1?xSe₂ was carried out at 850 °C, which is a relatively lower temperature compared to those in earlier reports, thus reducing secondary phase formation. An average Ga:In ratio of 62:38 (±3%) was measured using energy dispersive spectroscopy (EDS). As grown, a single crystal shows very high IR transmission of ～65% in the spectral range of 4000–600 cm^?1. There was no significant change in its IR transmission after annealing it at 500 °C for 20 days in vacuum in the presence of AgGa_xIn_1?xSe₂ powder. This indicates a low concentration of defects in the crystal. The results demonstrate that the improved new synthesis method for crystal growth was promising and that the quality of the crystal was good.     

Structural and Electrical Properties of Cd Doped InSe Thin Films

Polycrystalline Cd doped InSe thin films were obtained by thermal co‐evaporation of alpha‐In₂Se₃ lumps and Cd onto glass substrates at a temperature of 150°C. The films were annealed at 150°C and 200°C. The films were found to contain around 46% In, 47% Se and 7% Cd in weight. The films exhibited p‐type conductivity. The results of conductivity measurements have revealed that thermionic emission and variable range hopping are the two dominant conduction mechanisms, in the temperature ranges of 320‐160 K and 150‐40 K respectively. It was observed that above 240 K mobility is limited by the scattering at the grain boundaries. As the temperature decreases, thermal lattice scattering followed by the ionized impurity scattering dominate as the two main mechanisms controlling the mobility. Acceptor to donor concentration ratio was found to be slightly increasing due to annealing.     

Purification of ZnSiP2 and ZnSiAs2 by sublimation in a hermetically sealed system

In many cases the ternary compounds of the type ZnSiC₂^v are produced by gas phase transport or growth from solution. In this way prepared ternary substances contain binary compounds as a rule which are mixed or intergrown with the ternary compound. By sublimation of binary accompanying components in closed ampoules may be purified these ternary compounds. The separation of contaminants is complete and the loss of ternary substance is negligible. The inhibited decomposition of the ternary compounds during sublimation compared with binary compounds is probably caused by formation of an Si surface layer hindering diffusion of the highly-volatile elements of group II and V to the surface and their sublimation.     

Glass formation and properties of chalcogenide systems XXVI: Permittivity and the structure of glasses AsxSe1−x and GexSe1−x

Correlation between the real part of the dielectric constant and the structure of glasses in the system As_xSe_1?x and Ge_xSe_1?x is reported. The mole polarization is calculated using the Sellmeyer approximation neglecting the Lorentz field. The vibrationally caused part of the permittivity which is obtained by subtraction of the mole refraction reflects ordered states in the investigated series. Besides the known crystalline compounds As₂Se₃ and As₄Se₄ the formation of the vitreous AsSe₃ and As₃Se₂ from the liquid state has to be supposed. In the system Ge_xSe_1?x the formation of the compounds GeSe₂ and Ge₂Se₃ is completed by GeSe₄ which as Ge₂Se₃ obviously only exists in the non-crystalline state. GeTe₄ has been reported as a metastable crystalline phase. The temperature dependence of ?_r of vitreous As₂Se₃ is tentatively interpreted in terms of the dipole orientation caused by conversion of the charge in valence alternation pairs.     

119Sn Mössbauer studies of glassy and crystalline compounds in the chalcogenide system SeSnAs

¹¹⁹Sn Mössbauer measurements have been carried out on 18 chalcogenide glasses of different composition in the system SeSnAs. In all cases tin is four-coordinated and appears to be tetrahedrally surrounded by selenium. Two of the glasses (Se₆₀Sn₃As₃₇ and Se₄₇Sn₃As₅₀) were crystallized by heat treatment, and their Mössbauer spectra have been measured as a function of crystallization temperature and annealing time. As a result of the heat treatment, crystalline SnSe and SnSe₂ are precipitated. The amount of each compound is determined by the composition of the original glass and the remaining glassy or crystalline phase (As₂Se₃ and As₄Se₄). The degree of the crystallization depends on the temperature and the annealing time, but not the mass ratio of the tin selenides formed.     

Structural and Electrical Characterization of Ag3Ga5Te9 and Ag3In5Se9 Crystals

X-ray powder diffraction studies revealed that Ag₃Ga₅Te₉ and Ag₃In₅Se₉ crystallize in orthorhombic and tetragonal systems, respectively. The temperature dependent conductivity and Hall effect measurements have been carried out between 65—480 K. Ag₃Ga₅Te₉ exhibits p-type conduction with a room temperature conductivity of 4.3 × 10^—4 (Ω · cm)^—1 and mobility less than 1 cm²/V · s. Ag₃In₅Se₉ was identified to be n-type with room temperature conductivity 7.2 × 10^—5 (Ω · cm)^—1 and mobility 20 cm²/V · s. From temperature dependence of the conductivity three different impurity ionization energies were obtained for both compounds. The anomalous behavior observed in the temperature dependence of mobility was attributed to the different features of the microstructure.     

Crystal Data,Electrical Resisitivity and Mobility in Cu3In5Se9 and Cu3In5Te9 Single Crystals

X-ray powder diffraction data were obtained for Cu₃In₅Se₉ and Cu₃Te₉, which were found to crystallize in orthorhombic and tetragonal systems, respectively. The electrical resistivities and Hall mobilities of these compounds were investigated in the temperature range 35–475 K. Cu₃In₅Se₉, was identified to be n-type with a room temperature resistivity of 3 × 10³ Ω·cm which decreases with increasing temperature. For T < 65 K impurity activation energy of 0.03 eV and for T > 350 K onset of intrinsic conduction yielding a band gap energy of 0.99eV were detected. The neutral impurity scattering was found to dominate at low temperatures, while in the high temperature region thermally activated mobility was observed. Cu₃In₅Te₉ exhibits p-type conduction with a room temperature resistivity of 8.5 × 10⁻³ Ω·cm decreasing sharply above 400 K and yielding an impurity ionization energy of 0.13 eV. The temperature dependence of mobility indicates the presence of lattice and ionized impuritiy scattering mechanisms above and below 160 K, respectively.     

Phase equilibria and crystal chemical relations in copper-nickel-selenium system

Phase equilibria in the copper-nickel-selenium system has been investigated using x-ray diffraction and scanning electron microscopy. Ternary isotherms at 703 and 573 K show interesting differences. In the Cu-Se system, Cu₃Se₂, CuSe, and CuSe₂ phases decompose at higher temperatures. Only two phases viz., Cu_2-xSe and Cu₂Se are stable at 703 K. Solid solubility of nickel in these stable phases is ≈2 at %. Tetragonal Ni₃Se₂ phase has a solid solubility of about 8 at % copper in the ternary system. At 573 K, NiSe phase dissolves ≈5 at % copper. Rapid quenching of alloys on the Cu₂Se-Ni₃Se₂ quasi-binary section resulted no change in crystal structure. Phase relations and crystal chemistry of the system has been discussed in detail.     

Diffusion couple studies of the Ti‐Bi‐Zn system

The system Ti‐Bi‐Zn has been investigated using diffusion couples consisting of solid Ti and liquid (Bi+Zn) phase. The diffusion paths at 400, 500, 700 and 800 °C have been traced by means of electron microprobe analyses. The growth constants of the diffusion layers are roughly assessed. The phase diagram data obtained in this investigation are compared with previous studies of equilibrated alloys. The existence of the ternary compound TiBiZn has been confirmed. The formation of another phase with approximate formulae Ti₄Bi₃Zn to Ti₉Bi₇Zn₄ has been observed at high temperatures. The latter compound as well as the ternary extension of the Ti_XBi_Y (X ≈ 5, Y ≈ 6) phase react easily with air. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Devitrification characteristics of GexSe1−x glasses

Amorphous Ge_xSe_1?x compounds have been prepared and carefully characterized in the range 0 ? x ? 0.43 (density and micro-hardness measurements and DTA experiments). By heating samples from the amorphous phase, the crystallization process has been investigated for 0.15 ? x ? 0.30. An immiscibility gap in the vitreous region is determined by optical microscopy, from phase-separation observations; moreover, a new metastable crystalline phase appearing as an intermediate step between phase separation and stable GeSe₂ is described.     

Crystal structure of Ga<Subscript>0.5</Subscript>In<Subscript>1.5</Subscript>Se<Subscript>3</Subscript> solid solution

A solid solution of the GaIn₃Se₆ (2Ga_0.5In_1.5Se₃) composition with a hexagonal lattice (a = 7.051(3) Å, c = 19.148(2) Å, sp. gr. P6₁, z = 6, V = 824.4332(4) ų, ρ = 5.379(2) g/cm³) has been synthesized as a result of alloying Ga, In, and Se elements with a metal ratio of 1: 3. It was established that six out of nine In atoms in the lattice are located in a trigonal bipyramid, while the other three In atoms and three Ga atoms have a tetrahedral coordination.