Effect of Neutron Irradiation and Annealing on the Intensity of the Copper Related 1.01 eV Emission Band in n-type GaAs

Effect of neutron irradiation (E = 2 MeV, ϕ ≤ 10¹⁵ n/cm²) and subsequent annealing (T ≤ 700 °C, t = 30 min) on the intensity of the copper-related peaked at hvm =1.01 eV emission band in n-type GaAs (n₀ = 2 × 10¹⁸ cm⁻³) is studied. A strong irradiation-induced increase of the above emission intensity was observed testifying about the irradiation-stimulated growth in the concentration of copper-related 1.01 eV radiative centres (Cu_GaV_As pairs). A model is presented to explain this effect.     

Effect of Fast Electron Irradiation and Annealing on the Luminescence in GaAs(Zn) crystals. Irradiation-induced 1.26 and 1.39 eV Emission Bands

The effect of 2.2 MeV electron irradiation and subsequent annealings on the photoluminescence in zinc-doped p-type GaAs crystals is studied and analyzed. Rather strong emission bands peaked at hv_m (77 K) near 1.26 eV (induced by electron irradiation) and 1.39 eV (induced by annealing of irradiated crystals) are observed. Evidence is presented that the 1.26 and 1.39 eV emission bands occur due to radiative electronic transitions in As_iZn_Ga and V_AsZn_Ga pairs induced by irradiation and annealing of irradiated crystals, accordingly. The observed variations in the intensities of the 1.26 and 1.39 eV emission bands upon irradiation and subsequent annealings of GaAs(Zn) crystals are explained in terms of irradiation and annealing-induced variations in the amount of 1.26 and 1.39 eV radiative centres resulting from: a) the effective interaction of mobile radiation-induced defects in the arsenic sublattice with zinc atoms leading to the formation of As_iZn_Ga and V_AsZn_Ga pairs; b) the thermal dissociation of As_iZn_Ga and V_AsZn_Ga pairs on individual components.     

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.     

Irradiation plus annealing-induced 1.20 eV emission band in p-type GaAs

The effect of 2.2 MeV electron irradiation and subsequent annealings on the luminescence of tellurium-compensated p-type GaAs crystals is studied and analyzed. A comparatively strong emission band peaked at hv_m near 1.20 eV (induced by radiative electron recombination in Te_AsV_Ga pairs) appears in irradiated annealed (at T ≧ 250 °C) compensated p-type GaAs. The data obtained testify about the following: a) electron irradiation of GaAs creates stable (at T ≦ 200 °C) defects not only in the arsenic sublattice of GaAs, but in its gallium sublattice too; b) radiation plus annealing (r.p.a.)-induced Te_AsV_Ga pairs are characterized by a rather high (compared to that for grown-in Te_As V_Ga pairs) probability of electron radiative transitions in them. The electrical characterization of the r.p. a.-induced 1.20 eV radiative centres (Te_AsV_Ga pairs) is given.     

The molecular and crystal structure of 2-oxo-1-pyrrolidine-acetamide

C₆H₁₀N₂O₂, P1 , a = 6,607(2) Å, b = 8,538(2) Å, c = 6,392(2) Å, α = 102,43(2)°, β = 91,11(2)°, y = 79,82(2)°, V = 349,1 ų, Z = 2, D_m = 1,36 g × cm⁻³, D_x = 1,35 g × × cm⁻³, MoKα radiation, λ = 1.71069 Å, μ(MoKα) = 1.11 cm⁻¹. The structure was solved by direct methods. The parameters were refined by full matrix least squares technique to a final R = 0.088 for 834 reflections with ∥F₀∥ > 4σ(F₀). The dihedral angle between the least-squares plane through the pyrrolidine ring and that through the acetamide group is 90.4°. The N H … O hydrogen bonds connect molecules to form bands parallel to the z axis.     

The growth of high-quality MCT films by MBE using in-situ ellipsometry

The ellipsometry and RHEED study of high-quality MCT films grown on (112)- and (130) CdTe and GaAs by MBE was carried out. The dependence of the ellipsometric parameter ψ on MCT composition is evaluated. It was shown that such parameters as growth rate, the surface roughness, initial substrate temperature, and film composition may be measured by the in-situ ellipsometry. The appearance of surface roughness was observed in the initial stage of MCT growth under various compositions (x_CdTe = 0 ÷ 0.4). The further growth at optimum conditions leads to the smoothing of the surface and supplies us with high-quality MCT films. The concentration, mobility, and life time of carriers in MCT films were respectively: n = 1.8 × 10¹⁴ ÷ 8.2 × 10¹⁵ cm⁻³, μ_n = 44000 ÷ 370000 cm² V⁻¹ s⁻¹, τ_n = 40 ÷ 220 ns; p = 1.8 × 10¹⁵ ÷ 8.4 × 10¹⁵ cm⁻³, μ_p = 215 ÷ 284 cm² V⁻¹ s⁻¹, τ_p = 12 ÷ 20 ns.     

Incorporation of nitrogen into galliumarsenide grown by chloride VPE

The incorporation of nitrogen into GaAs in the halide-VPE system using NH₃ as the doping source is investigated. The concentration of incorporated N depends on the NH₃ flow rate and increases with decreasing deposition temperature. Concentrations up to 6 × 10¹⁷ cm⁻³ could be detected far above the calculated equilibrium value. By a comparison of SIMS-data with those obtained from IR it is found that most of the N-atoms are situated substitutionally on As lattice sites. Normal-pressure 2 K photoluminescence measurements show N-related luminescence peaks at 1.508 and 1.496 eV. Most probably this luminescence arises from complexes of N with undeliberately introduced impurities. For the 1.508 eV center a complex Si_Ga-N_As is discussed. — A new N-related metastable deep center with the energy levels E_c-0.33, E_c-0.41, and E_c-0.68 eV could be found by DLTS.     

Temperature dependence of electrical conductivity and hall effect of Ga2Se3 single crystal

Electrical conductivity (σ) and Hall coefficient (R_H) of single crystal grown from the melt have been investigated over the temperature range from 398 K to 673 K. Our investigation showed that our samples are p-type conducting. The dependence of Hall mobility an charge carrier concentration on temperature were presented graphically. The forbidden energy gap was calculated and found to be 1.79 eV. The ionization energy of impurity level equals 0.32 eV approximately. At 398 K the mobility equals to 8670 cm² V⁻¹ s⁻¹ and could described by the law μ = aTⁿ (n = 1.6) in the low temperature range. In the high temperature range, adopting the law μ = bT^–m (as m = 1.67), the mobility decreases. This result indicates that in the low temperature range the dominant effect is scattering by ionized impurity atoms, whereas in the high temperature range the major role is played by electron scattering on lattice vibrations (phonons). At 398 K the concentration of free carriers showed a value of about 1.98 × 10⁷ cm⁻³.     

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.     

Investigations for Sn diffusion in Pb1−xSnxTe and PbTe

By annealing Pb_1−xSn_xTe and PbTe isothermally in a quartz ampoule Sn diffused from Pb_1−xSn_xTe into PbTe. The profiles obtained have been investigated by means of an electron beam microanalyser, and the coefficients of diffusion have been determined at various temperatures. The diffusion of Sn can be explained by the expressions: D_PbSnTe = 1.5 · 10⁻¹ exp (−1.8 eV/kT) cm² s⁻¹ (0,14 < x < 0,18) D_PbTe = 5,5 · 10⁻⁴ exp (−1.5 eV/kT) cm² s⁻¹. N-type layers are observed at the surface of Pb_1−xSn_xTe specimens.     

Crystal Structure of a Complex of Sarcosine with Barium Chloride

Single crystals of sarcosine barium chloride tetrahydrate were crystallised from a saturated aqueous solution containing stoichiometric amounts of sarcosine and barium chloride, in 2: 1 proportion. The intensity data were collected using a CAD-4 diffractometer with graphite monochromated MoKα radiation. The crystal data are as follows: a = 7.235(1) Å, b = 10.668(4) Å, c = 15.686(3) Å, V = 1210.7 ų, F.W. = 369.33, d_expt, = 2.02 g · cm⁻³, d_calc = 2.026 g · cm⁻³, Z = 4 and the space group is P2₁2₁2₁. The structure has been solved to an R value of 0.02 for all the 1239 reflections with I > 2σ(I). The sarcosine molecule exists as zwitterion in the structure. The barium ion is found to have 10-fold coordination with nine oxygens and a chlorine taking part in coordination. All the water oxygens and chlorines take part in hydrogen bonds except carboxyl oxygens.     

An X-ray diffraction refinement of the structure of natural thomsonite

Thomsonite Na₂Ca₄Al₁₀Si₁₀O₄₀, orthorhombic Pncn, a = 1.3124 nm, b = 1.3078 nm, c = 0.662 nm, V = 1.1369 nm³, Z = 2, D_m = 2.30, D_c = 2.26, μ = 12.4 cm⁻¹. The average length of the bond T–O = 0.1685 nm. The final R-value for 456 independent observed reflections is 0.085.     

Growth of Zn3As2 on GaAs by liquid phase epitaxy and their characterization

Zn₃As₂ epitaxial layers were grown on GaAs (1 0 0) substrates by liquid phase epitaxy (LPE) using Ga as the solvent. Zinc mole fraction in the growth melt was varied from 1.07×10^?2 to 6×10^?2. X-ray diffraction spectrum exhibits a sharp peak at 43.3° characteristic of Zn₃As₂ crystalline layer. The peak intensity increases with increase in zinc mole fraction in the growth melt. The compositions of the as-grown Zn₃As₂ layers were confirmed by energy dispersive X-ray (EDX) analysis. Surface morphology was studied using scanning electron microscopy (SEM) and the thickness of the epilayers was also determined. The Hall measurements at 300 K indicate that Zn₃As₂ epilayers are unintentionally p-doped. With an increase of zinc mole fraction in the growth melt, carrier concentration increases and carrier mobility decreases. Infrared optical absorption spectroscopy showed a sharp absorption edge at 1.0 eV corresponding to the reported band gap of Zn₃As₂.     

Static Disorder in Hexagonal Crystal Structures of C60 at 100 K and 20 K

C₆₀ · 2C₈H₁₀ (100 K): hexagonal space group P6₃, a = 23.694(4), c = 10.046(2) Å, V = 4884(2) ų, D_x = 1.903 g cm⁻³, Z = 6, F(000) = 2856, γ(CuKa) = 1.54178 Å, μ = 0.84 mm⁻¹. C₆₀ · 2C₈H₁₀ (20 K): hexagonal space group P6₃, a = 23.67(1), c = 10.02(1) Å, V = 4862(6) ų, D_x = 1.912 g cm⁻³, Z = 6, F(000) = 2856, γ(CuKa) = 1.54178 Å, μ = 0.84 mm⁻¹. The structures were determined by Patterson syntheses and rigid-body refinements. The C₆₀ molecules show two orientations with one molecular centre in common. The solvent molecules are disordered too. Static disorder could not be overcome or influenced by cooling down. A coordination number of 10 was found for the fullerene molecules.     

Crystal and molecular structures of N-alkyl-N,N-dimethyl-3-(heptamethyltrisiloxan-3-yl) propylammonium bromides

C₁₆H₄₂NO₂Si₃Br: M_r = 444.76, monoclinic space group P 2₁/c, a = 23.300(8), b = 8.918(4), c = 13.403(2) Å, β = 101.69(4)°, V = 2727(1) ų, D_x = 1.08 Mgm⁻³, D_exp = 1.06 Mgm⁻³, Z = 4, F(000) = 932, λ(MoKα) = 0.71069 Å, μ = 16.3 cm⁻¹. The crystal structure was determined by direct methods and refined by least-squares procedure to the discrepancy factor R = 0.117. C₁₅H₄₀NO₂ Si₃Br: M_r = 430.34, monoclinic space group P2₁/c, a = 23.460(4), b = 8.518(2), c = 13.403(2) Å, β = 102.03(2)°, V = 2619(1) ų, D_x = 1.09 Mgm⁻³, D_exp = 1.07 Mg⁻³, Z = 4, F (000) = 920, λ(MoKα) = 0.71069 Å, μ = 33.9 cm⁻¹. The crystal structure was determined by least-squares refinement of the structure model derived from structure determination of C₁₆H₄₂NO₂·Si₃Br to the discrepancy factor R = 0.099. C₁₆H₄₂NO₂Si₃Br: Daten siehe oben. C₁₅H₄₀NO₂Si₃Br: Daten siehe oben.     

Absorption and electrical conductivity of CaMoO4 crystals

The electrical conductivity σ of CaMoO₄ crystals was investigated between room temperature and 850°C. The mobility v_v and the diffusion coefficient D_v of the O⁻ ion vacancies have been derived from σ: v_vT = 3300 exp (−1.52 eV/kT) cm² K/Vs, D_v = (0.1…1) × exp (−1.52 eV/kT) cm²/s. An absorption occuring in crystals which are reduced or X-irradiated at low temperatures is dichroitic and caused by Mo⁵⁺ ions. For measurement in c direction the oscillator strength of the 680 nm absorption band is found to be about 0.1.     

Crystal and Molecular Structure of Tosyl Pyrrolidine-2-Methanol (C12H17SO3N)

C₁₂H₁₇SO₃N, M_r = 255.33, Orthorhombic, P2₁2₁2₁, a = 11.703(1) Å, b = 14.797(3) Å, c = 14.971(2) Å, V = 2592.52 ų, Z = 8, D_m = 1.309 Mgm⁻³, D_c = 1.308 Mgm⁻³, mμ = 21.57 cm⁻¹, F(000) = 1088, T = 290 K, final R = 0.080 for 2416 unique reflections. There are two crystallographically independent molecules in the unit cell of the title compound.     

Impurity diffusion of 114In in Cu

Using the tracer-standard sectioning technique the impurity diffusion of indium in copper has been investigated in the temperature range from 798.1 to 1081.0°C. For the frequency factor and the activation energy, respectively, the following values were determined: D₀₂ = 1.87 cm² · s⁻¹; Q₂ = 2.034 eV. The results are compared with predictions of theoretical models of the impurity diffusion in metals.     

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.     

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.