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.     

Electric Characterization of Indium Sesquiselenide Single Crystals

Conductivity, Hall-effect measurements were performed on δ-phase In₂Se₃ single crystals, grown by the Bridgman method over the temperature range 150–428 K, in the directions perpendicular and parallel to the c-axis. The anisotropy of the electrical conductivity and of the Hall coefficient of n-type In₂Se₃ had been investigated. The values of the Hall coefficient and electrical conductivity at room temperature spreads from an order of R_H11 = 1.36 × 10⁴ cm³/coul, σ₁₁ = 4.138 × 10⁻³ Ω⁻¹ cm⁻¹ and R_H = 66.55 × 10⁴ cm³/coul, σ = 0.799 × 10⁻³ Ω⁻¹ cm⁻¹ for parallel and perpendicular to c-axis, respectively. The temperature dependence of Hall mobility and carrier concentration are also studied.     

Semiconducting Properties of TI2Te3 Single Crystals

Electrical conductivity and Hall effect measurements were performed on single crystals of TI₂Te₃ to have the general semiconducting behaviour of this compound. The measurements were done at the temperature range 160–350 K. All crystals were found to be of p-type conductivity. The values of the Hall coefficient and the electrical conductivity at room temperature were 1.59 × 10³ cm³/coul and 3.2 × 10⁻² ω⁻¹ cm⁻¹, respectively. The hole concentration at the same temperature was driven as 39.31 × 10¹¹ cm⁻³. The energy gap was found to be 0.7 eV where the depth of impurity centers was 0.45 eV. The temperature dependence of the mobility is discussed.     

Enhancement of thermoelectric efficiency in vapor deposited Sb2Te3 and Sb1.8In0.2Te3 crystals

Pure and indium doped antimony telluride (Sb₂Te₃) crystals find applications in high performance room temperature thermoelectric devices. Owing to the meagre physical properties exhibited on the cleavage faces of melt grown samples, an attempt was made to explore the thermoelectric parameters of p‐type crystals grown by the physical vapor deposition (PVD) method. The crystal structure of the grown platelets (9 mm× 8 mm× 2 mm) was identified as rhombohedral by x‐ray powder diffraction method. The energy dispersive analysis confirmed the elemental composition of the crystals. The electron microscopic and scanning probe image studies revealed that the crystals were grown by layer growth mechanism with low surface roughness. At room temperature (300 K), the values of Seebeck coefficient S (⊥ c) and power factor were observed to be higher for Sb_1.8In_0.2Te₃ crystals (155 μVK⁻¹, 2.669 × 10⁻³ W/mK²) than those of pure ones. Upon doping, the thermal conductivity κ (⊥ c) was decreased by 37.14% and thus thermoelectric efficiency was improved. The increased figure of merit, Z = 1.23 × 10⁻³ K⁻¹ for vapour grown Sb_1.8In_0.2Te₃ platelets indicates that it could be used as a potential thermoelectric candidate.     

Generation of VGaTeAsVAs Complexes in Tellurium-doped n-type GaAs by Low-temperature Annealing

It is shown that low-temperature annealing (T= 425 to 625 °C, t ⩾ 0.5 h) of tellurium-doped n-type GaAs crystals (n₀ = 2 × 10¹⁸ cm⁻³) leads to a generation of V_GaTe_AsV_As complexes as a result of a diffusion of arsenic vacancies to V_GaTe_As complexes or arsenic and gallium vacancies to isolated tellurium atoms. The observed regularities of generation of V_GaTe_AsV_As complexes as the annealing temperature and the annealing time are varied are well explained by the proposed model of diffusion-limited formation of V_GaTe_AsV_As complexes.     

Electrical and photoconductive properties of GaS0.75Se0.25 mixed crystals

The conductivity, mobility, photoconductivity and photo response measurements in GaS_0.75Se_0.25 mixed crystals were carried out in the temperature range of 150‐450 K. The room temperature conductivity, mobility and electron concentration values were 10^‐9 (Ω‐cm)^‐1, 48 cm²V^‐1s^‐1 and ∼10⁹ cm^‐3, respectively. Two donor levels were obtained from temperature‐dependent conductivity and carrier concentration, located at energies of about 755 and 465 meV below the conduction band. Single donor‐single acceptor analysis yields the same donor level at 465 meV with donor and acceptor concentrations of 8.7 × 10¹⁴ and 5.3 × 10¹³ cm^‐3, respectively. The mobility‐temperature dependence shows that ionized impurity scattering dominates the conduction up to the temperature 310 K with different temperature exponent, while above this critical temperature; the phonon scattering is dominant conduction mechanism. From the photo‐response spectra, the maximum photocurrent was observed for all the samples at 2.42 eV, and varied slightly with temperature. Moreover, the photocurrent‐light intensity dependence in these crystals obeys the power law, I_ph ∝ ϕ^γ with γ between 1.7 and 2.0 for various applied fields and temperatures. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization and Thermoelectric Power of Tl2Te3 Single Crystals

Thermoelectric power (TEP) of Tl₂Te₃ was measured in the temperature range from 150 to 480 K. The crystal was found to have a p-type conductivity throughout the whole range of temperature. The effective masses of holes and electrons were determined at room temperature and found to be m = 1.1 × 10⁻³⁴ kg and m = 1.72 × 10⁻³⁵ kg, respectively. Also at the same temperature the mobility μ_p was found to be 1737.8 cm²/V.s and μ_n was 3962.2 cm²/V.s. The hole and electron diffusion coefficients were obtained as 44.84 cm²/s, and 102.23 cm²/s. The relaxation times for holes and electrons were calculated and yielded the values τ_p = 1.19 × 10¹² s and τ_n = 4.25 × 10¹³ s, respectively.     

Direct measurement of isothermal compressibility of amorphous semiconductors

The isothermal compressibilities of the chalcogenide glasses Te₁₅Ge₃As₂, Te₁₅Ge₂As₃ and As₂Se₃ have been measured to 5 kbar by direct measurement of the change in sample length using a differential transformer placed inside the hydrostatic pressure vessel. Calibration data was obtained from the measurement of the compressibilities of alkali halide single crystals. For Te₁₅Ge₃As₂, the isothermal compressibility was found to be 6.00 × 10^?12 ? 0.7 × 10^?22P cm²/dyne; for Te₁₅Ge₂As₃, 5.58 × 10^?12 + 0.3 × 10^?22P cm²/dyne; for As₂Se₃, 6.30 × 10^?12 ? 0.8 × 10^?22P cm²/dyne where P is the pressure in dynes/cm². Errors are near 5%.     

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.     

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)     

The field effect in amorphous chalcogenides: An investigation of localized states and electronic transport

The temperature dependence of the field effect response permits an unambiguous determination of the identity of those states responsible for electrostatic screening in the amorphous chalcogenides. We observe (1) in As₂Te₃, field effect screening by localized states at the Fermi level at low temperatures (～ 10¹⁹ cm^?3 eV^?1) and by mobile charge carriers (～ 10¹⁸ cm^?3 at 300 K) at high temperatures, and a transition from p-type to two-carrier (primarily n-type) conductivity as the temperature is raised above ～320 K; (2) in As₂SeTe₂, screening by mobile charge carriers (～ 10¹⁸ cm^?3 at 300 K) with strongly type conductivity; (3) in As₂Se₂Te, screening by localized states at the Fermi level (～ 10¹⁹ cm^?3 eV^?1) with strongly p-type conductivity; and (4) in Sb₂Te₃, a very high density of localized states at the Fermi level (～ 2 × 10²⁰ cm^?3 eV^?1) with both electron and hole contributions to the conductivity. Correlation with thermoelectric power results suggests that the p-type conductivity in As₂Te₃ is due to near-equal contributions from two processes: hopping in localized states plus extended state conduction. Aging and annealing behavior is described with the aid of a “chaotic potential model” that appears to be able to account for large changes in mobile carrier density that leave the conductivity unaltered.     

Thermoelectric properties of indium sesquiselenide single crystals

Single crystals of δ-In₂Se₃ were prepared in the solid state laboratory at Qena-Egypt, by means of Bridgman technique. The temperature dependence of the thermal e.m.f. α in the temperature range from 205 K up to 360 K of In₂Se₃ was studied. The δ-phase In₂Se₃ sample appeared to be n-type. The ratio of the electron and hole mobilities are found to be μ_n/μ_p = 1.378. The effective masses of charge carriers are m = 1.3 × 10⁻³⁰, m = 8.27 × 10⁻³¹ kg for holes and electrons, respectively. The diffusion coefficient was estimated to be D_n = 3.37 cm²/s and D_p = 2.45 cm²/s for both electrons and holes, respectively. The mean free time between collision can be deduced to be τ_n = 70 × 10⁻¹⁶ s and τ_p = 8 × 10⁻¹⁴ s for both electrons and holes. The diffusion length of the electrons and holes are found to be L_n = 1.5 × 10⁻⁷ cm and L_p = 4.4 × 10⁻⁷ cm.     

Infrared and Raman spectroscopy of mullite‐type Bi2Ga4O9

Mullite‐type Bi₂Ga₄O₉ single‐crystals were grown by the top‐seeded solution growth (TSSG) method and investigated by vibrational spectroscopy. Polarised IR specular reflectance and attenuated total reflectance (ATR) spectra, as well as polarised micro‐Raman spectra were acquired at room temperature. Powder IR spectra of sol‐gel‐derived samples were also recorded. Using model calculations and comparison to other mullite‐type compounds, bands at ∼ 850 – 400 cm^‐1 could be assigned to stretching and bending vibrations of the structural GaO₄ and GaO₆ units. Low‐energetic modes were attributed to motions involving Bi atoms. The IR spectra of Bi₂Ga₄O₉ display close similarities to those of the mullite‐type alkali gallates (9Ga₂O₃ · Rb₂O), while their differences to those of mullite sensu stricto (3Al₂O₃ · 2SiO₂ and 2Al₂O₃ · SiO₂, repectively) are assigned to Si‐O stretching vibrations of the corresponding tetrahedral units. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of the nature of point defects in in Te-doped gallium antimonide

Precision lattice constant and density measurements held on gallium antimonide single crystals grown from stoichiometric melts showed that doping of such crystals with Te lead to the intensification of Ga-supersaturated solid solution decomposition process with initial Frenkel defect (Ga_i + V_Ga) production. It is supposed that Te_sb — simple donors form complexes with V_Ga which are believed to be acceptors. Doping of GaSb with Te up to the levels above 2 · 10¹⁸ cm⁻³ leads to partial decomposition of GaSb(Te) solid solution supersaturated with Te.     

Single Crystal Growth and Electrical Properties of Gallium Monotelluride

Single crystals of GaTe were prepared in our laboratory by a special modified Bridgman technique method. Measurements of the electrical conductivity and Hall effect between 210 and 450 K were carried out on GaTe samples in two crystallographic directions. The Hall coefficient is positive and varies with the crystallographic direction. A unique mobility behaviour and strong anistropy in the carrier mobility were observed. The Hall mobilities parallel and perpendicular to the C-axis, at room temperature, were 12 cm/V · s and 25.12 cm²/V ·s, respectively. The free carrier concentration lies between 10¹³ − 10¹⁴ cm⁻³ at room temperature.     

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.     

Concentration distribution of Nd3+ In Nd:Gd3Ga5O12 crystals studied by optical absorption method

Nd:Gd₃Ga₅O₁₂ crystals with different concentrations of Nd³⁺ were grown by Czochralski method, their absorption spectra were measured at room temperature. By using the optical absorption method, the effective distribution coefficient k_eff for Nd³⁺ in GGG was fitted to be 0.40±0.01, which is higher than that of Nd³⁺ in YAG. The 808nm absorption cross‐section was calculated to be 4.0±0.2×10^‐20cm^‐2. The lengthways and radial concentration distribution of Nd³⁺ in the crystals were also analyzed and discussed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ionic conductivity of Li2OB2O3 thin films

The ionic conductivity of evaporated Li₂OB₂O₃ thin films has been studied. These thin films were found to show a considerably high ionic conductivity of 1 × 10^?7 Ω^?1 cm^?1 at room temperature. The conductivity increases with increasing Li content and exhibits a maximum value near 3Li₂O·B₂O₃. The structure of these films was determined using infrared absorption and laser Raman scattering spectroscopy. Using the results, the correlation between structure and conductivity is also discussed.     

Zur Realstruktur von Ga1–xInxAs LPE-Schichten

Ga_1–xIn_xAs epitaxial layers (0.02 ≦ × ≦ 0.12) are grown on (111)-oriented GaAs substrates from nonstoichiometric melts. The etch pit densities – determined by chemical etching – yield values between 2 · 10⁵ cm⁻² and 3 · 10⁷ cm⁻² and were found to be dependent on composition, layer thickness and cooling rate. X-ray topography of cleaved {110}-planes gives information on layer quality and indicates the existence of stress in the substrate lattice near the heterojunction. The validity of Vegard's law in the investigated concentration range was confirmed by X-ray determination of the lattice constants. The half width of double crystal spectrometer rocking-curves, the epd and the relative intensity of photoluminescence show similar dependence on the composition of the mixed crystal layers.     

Crystal growth and spectral properties of Nd:Ca5(BO3)3F

A neodymium doped Ca₅(BO₃)₃F single crystal with size up to 51×48×8 mm³ has been grown by the top seeded solution growth (TSSG) technique with a Li₂O‐B₂O₃‐LiF flux. The spectra of absorption and fluorescence were measured at room temperature. According to Judd‐Ofelt (J‐O) theory, the spectroscopic parameters were calculated and the J‐O parameters Ω₂, Ω₄, Ω₆ were obtained as follows: Ω₂ = 1.41×10⁻²⁰cm², Ω₄ = 3.18×10⁻²⁰cm², Ω₆ = 2.11×10⁻²⁰cm². The room temperature fluorescence lifetime of NCBF was measured to be 51.8 μs. According to the J‐O paramenters, the emission probabilities of transitions, branching ratios, the radiative lifetime and the quantum efficiency from the Nd^{3+ 4}F_3/2 metastable state to lower lying J manifolds were also obtained. In comparasion with other Nd‐doped borate crystals, the calculated and experimental parameters show that NCBF is a promising SFD crystal.