Microdeformations of the crystal lattice of PbTe1 − x Br x solid solutions

Microdeformations of the crystal lattice of PbTe_{1 ? x} Br _x solid solutions depending on the bromine content are determined by analysis of the physical broadening of X-ray reflections. It is found that they increase with the introduction of bromine from 0.188% (for undoped PbTe) to 0.283% for PbTe_{1 ? x} Br _x at x = 0.02. The microstrains remain constant with a further increase in the bromine content.     

Evidence of the third (A +) level of the mercury vacancy in Cd x Hg1 ? x Te

The existence of a previously unknown shallow acceptor level (depth of ??1 meV), which belongs to the intrinsic defect of the semiconductor crystal rather than to the impurity, is found for Cd _x Hg_{1 ? x} Te compounds. It is concluded from analysis of the experimental data that this state is the third level of the mercury vacancy V _Hg, which emerges due to the capture of an additional hole (state A ⁺).     

Nature of the diamagnetic maximum in the temperature dependences of the magnetic susceptibility of crystals of (Bi2 ? x Sb x )Te3 alloys (0 < x < 1)

The temperature dependences of the magnetic susceptibility ?? of crystals of (Bi_{2 ? x} Sb _x )Te₃ alloys (0 < x < 1) are studied using a SQUID magnetometer in the temperature range from 2 to 400 K with the parallel and perpendicular orientations of the vector of magnetic field strength H relative to the trigonal axis of the crystal C ₃ (H ?? C ₃ and H ?? C ₃). It is found that the diamagnetic susceptibility of the samples with x = 0.2 (Bi_1.8Sb_0.2Te₃) and x = 0.5 (Bi_1.5Sb_0.5Te₃) increases in the range from 50 K to temperatures preceding the emergence of intrinsic conductivity (250 K). It is found that the diamagnetic maximum manifests itself in the same temperature range, in which an anomalous increase in the Hall coefficient is observed. It is shown that the nature of the diamagnetic maximum is associated with the nonparabolicity of the energy spectrum of light diamagnetic holes, a decrease in whose concentration is accompanied by a decrease in their effective masses, which provides an increase in the diamagnetic susceptibility with increasing temperature. These results are confirmed by the dynamics of the temperature variation in the resonance frequency of plasma oscillations of free charge carriers.     

Determination of the thickness and spectral dependence of the refractive index of Al x In1 − x Sb epitaxial layers from reflectance spectra

A nondestructive method for measuring the thicknesses of epitaxial layers of Al _x In_{1 ? x} Sb alloys based on interference effects in reflectance spectra measured in a wide wavelength range (1–28 μm) is implemented. The studied 0.9–3.3 μm thick Al _x In_{1 ? x} Sb layers are grown on highly lattice-mismatched GaAs substrates by molecular beam epitaxy. The found thicknesses are in good agreement with the independent data of scanning electron microscopy. The spectral dependence of the refractive index n(E) of Al _x In_{1 ? x} Sb layers is measured both for the regions of transparency and fundamental absorption. The refractive index for the case of E < E ₀ was calculated by a double-oscillator model using a refined experimental dependence of the band gap on the composition E ₀(x). The experimental data on the n(E) of Al _x In_{1 ? x} Sb for energies E > E ₀ are found based on the interference pattern.     

Width of the excitonic absorption line in Al x Ga1 − x as alloys

Experimental data on the width of the absorption line corresponding to the exciton ground state in high-quality samples of Al _x Ga_{1 ? x} As (x = 0.15) quasi-binary alloy, obtained by Seisyan et al. (2005), are analyzed. The line corresponding to the 1s state is divided into separate components taking into account strain-induced splitting; Lorentzian- and Gaussian-shape contributions to the absorption curve; and overlap with the continuum absorption band, which broadens with increasing temperature. Analysis of the integrated absorption, relying on the fact that the temperature dependence of the absorption is typical of exciton polaritons in media possessing spatial dispersion, was carried out with the following parameters: critical value of the dissipation damping of the exciton Γ_c = 0.32 meV and maximum value of the absorption coefficient K _max = 89.5 eV/cm. This analysis makes it possible to determine the homogeneous component of the line broadening, which, up to the critical temperature T _c = 155 K does not exceed 0.2 meV. It is found that the “natural” width of the 1s-exciton line does not exceed 2.6 meV at T = 1.7 K, which is in agreement with theoretical estimates. At T = 1.7–60 K, the inhomogeneous broadening of the exciton peak related to the exciton scattering and localization by fluctuations of the alloy composition exceeds contributions related to phonons and ionized impurities by more than an order of magnitude and is dominant, but does not affect the integrated absorption by excitonic polaritons.     

Relaxation features of the dielectric response of Cd1−x ZnxTe crystals grown from the melt

It is shown that the low-frequency dielectric response of Cd_1?x Zn_xTe crystals grown from the melt is controlled by macroscopic growth defects and their elastic and electric fields. An interconsistent realignment of these fields under the action of external forces changes the dielectric response, which reflects features of the large-scale potential-relief distortions.     

Effects of thermal annealing on the morphology of the AlxGa(1−x)N films

Effects of thermal annealing on the morphology of the Al_xGa_(1−x)N films with two different high Al-contents (x=0.43 and 0.52) have been investigated by atomic force microscopy (AFM). The annealing treatments were performed in a nitrogen (N₂) gas ambient as short-time (4 min) and long-time (30 min). Firstly, the films were annealed as short-time in the range of 800–950 °C in steps of 50–100 °C. The surface root-mean-square (rms) roughness of the films reduced with increasing temperature at short-time annealing (up to 900 °C), while their surface morphologies were not changed. At the same time, the degradation appeared on the surface of the film with lower Al-content after 950 °C. Secondly, the Al_0.43Ga_0.57N film was annealed as long-time in the range of 1000–1200 °C in steps of 50 °C. The surface morphology and rms roughness of the film with increasing temperature up to 1150 °C did not significantly change. Above those temperatures, the surface morphology changed from step-flow to grain-like and the rms roughness significantly increased.     

Effect of annealing on the electrical properties of Pb1 − x Mn x Te single crystals with excess tellurium

The electrical conductivity σ, Hall coefficients R, and thermopower α of Pb_0.96Mn_0.04Te (Te) single crystals annealed at 573 K for 120 h are investigated. It is shown that, in contrast to unannealed samples, the investigated samples exhibit n-type conductivity and metal-type dependences σ(T) in the temperature range 77–300 K. It is suggested that, upon annealing, a portion of the excess tellurium atoms occupy vacancies in the lead sublattice with the formation of new vacancies in the tellurium sublattice of the samples.     

Possibility of obtaining the (GaSb)1 − x (Si2) x films on silicon substrates by the method of liquid-phase epitaxy

Semiconductors - It is shown that it is possible to grow a continuous series of (GaSb)1 ? x (Si2) x (x = 0?1) alloys on silicon substrates by the method of liquid-phase epitaxy from a...     

On the resonant level of chromium in the rhombohedral and cubic phases of Pb1 − x − y Ge x Cr y Te alloys

The temperature dependences of the Hall coefficient (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) in Pb_{1 ? x ? y} Ge _x Cr _y Te alloys (x = 0.03–0.08, y ≤ 0.01) are studied. An increase in the absolute value of the Hall coefficient with an increase in temperature is found. This fact is indicative of a decrease in the concentration of free electrons as a result of the motion of the resonant level of chromium stabilizing the Fermi level relative to the conduction-band bottom. The temperature dependences of the Hall coefficient, in satisfactory agreement with the experimental ones, are calculated in the context of the two-band Kane dispersion law allowing for the structural phase transition upon increasing temperature. The energy position and temperature coefficients of the motion of the resonant level of chromium relative to the middle of the band gap in the rhombohedral and cubic phases are determined.     

Phase formation upon the interaction of thin films in the system Yb1 − x Sm x Te-As2Te3

Phase formation upon the interaction of thin Yb_{1 ? x} Sm _x Te (x = 0.02) and As₂Te₃ films obtained through their simultaneous and successive evaporation is studied. It is shown that the Yb_{1 ? x} Sm _x As₄Te₇ phase is formed upon interaction of the thin films at a temperature of 473 K and the Yb_1?x Sm _x As₂Te₄ phase at 503 K.     

Effect of Excess Na on the Morphology and Thermoelectric Properties of Na x Pb1−x Te0.85Se0.15

The thermoelectric properties of p-Na _x Pb_1?x Te_0.85Se_0.15, which possesses a high thermoelectric figure of merit due to band convergence, have been systematically investigated for increasing Na concentration (x = 0.01, 0.02, 0.03, 0.05, and 0.07) from room temperature to 773 K. For x values up to 0.03, the hole concentration increases with the Na concentration; however, for x ≥ 0.03, excess Na forms separate microstructures with needle- and plate-like shapes. At high concentrations (x = 0.05 and 0.07) both the number and size of these structures increase (over 10 μm). Differential scanning calorimetry identifies a phase change near 660 K in samples with x = 0.05 and 0.07, confirming the formation of microstructures; this phase change leads to a decrease in electrical resistivity. However, these microstructures do not significantly affect thermal transport, probably because they are too large to scatter phonons. The highest thermoelectric figure of merit, zT, value is 1.6, which is obtained at 760 K for x = 0.05, due to the low thermal conductivity and electrical resistivity.     

Structural and electronic properties of Si1 − x Ge x binary semiconducting alloys under the effect of temperature and pressure

Based on the empirical pseudo-potential method which incorporates compositional disorder as an effective potential, the band structure of Si_{1 ? x} Ge _x alloy are calculated for different alloy composition x. The effect of temperature and pressure on the electronic band structure of the considered alloy has been studied. Monotonic decreasing and increasing functions are obtained for the temperature and pressure dependent form factors respectively. Some physical quantities as band gaps, bowing parameters, and the refractive index of the considered alloy with different Ge concentration and under the effect of temperature and pressure are calculated. The results obtained are found in good agreement with the experimental and published data.     

Ionization of the sulfur-related DX Center in In 1 − x Ga x P in an electric field

Using deep-level transient spectroscopy and capacitance-voltage measurements, the effect of electric field on ionization of the sulfur-related DX center is investigated for n-In_{1 ? x} Ga _x P layers (x = 0.65) grown by vapor-phase epitaxy. It is shown that, upon increasing the electric field strength from 1.3 × 10⁴ to 1.9 × 10⁵ V/cm, the activation energy of the center decreases from ～0.38 to ～0.26 eV, and the ionization process is governed by multiphonon tunneling. By the estimated tunneling time of the defect, it is concluded that the DX center corresponds to a model of large lattice relaxation.     

First-principles investigation of the optical properties of CuIn(SxSe1–x)2

We optimized the lattice structure of sulfur-doped CuInSe₂ using first principles. The lattice constants for CuIn(S_xSe_1–x)₂ vary linearly with x according to a(x)=–0.02828x+0.58786 nm and c(x)=–0.05692x+1.1834 nm, which agree well with experimental data. The optical properties of CuIn(S_xSe_1–x)₂ were then systematically investigated using first-principles calculations with the HSE06 functional. We present data for the complex dielectric function, refractive index, extinction coefficient, reflectivity index, absorption coefficient, and optical bandgap for CuIn(S_xSe_1–x)₂. The optical bandgap E_g obtained from the absorption coefficient is 1.07 eV for CuInSe₂ and 1.384 eV for CuInS₂. These values are very close to experimental results, indicating that first-principles calculations can yield accurate bandgap values. The optical bandgap of CuIn(S_xSe_1–x)₂ increases linearly with the sulfur concentration according to E_g=0.3139x+1.0825 eV.     

Thermoelectric Properties of the Entire Composition Range in Mg2Si0.9925−x Sn x Sb0.0075

Eleven samples of nominal composition Mg_2.2Si_0.9925?x Sn _x Sb_0.0075 with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.9925 were prepared by induction melting, ball milling, and spark plasma sintering. Hall effect, resistivity, Seebeck coefficient, and thermal conductivity measurements were conducted from room temperature to 400°C. Six of the samples were investigated for thermal stability by measuring powder x-ray diffraction while heating to 400°C. All samples were stable in air during the ～12-h-long data collection, except for Mg_2.2Sn_0.9925Sb_0.0075, which showed development of an elemental Sn phase after heating. The lattice parameter of each sample was extracted through Rietveld refinement and revealed a linear dependency on nominal composition. Measurement of top and bottom of the pellets exhibited systematic differences in lattice parameter and Seebeck coefficient, indicating that stoichiometry gradients are created during sintering.     

On the preparation and photoelectric properties of Tl1–x In1–x Sn x Se2 (x = 0.1–0.25) alloys

The technological conditions for growing single crystals of Tl_1–x In_1–x Sn _x Se₂ (x = 0.1–0.25) alloys are developed. The spectral distribution of the photoconductivity of the grown crystals at T = 300 K and thermally stimulated conductivity are studied. The effect of In³⁺cation substitution with Sn⁴⁺ in Tl_1–x In_1–x Sn _x Se₂ (x = 0.1–0.25) alloys on their photoelectric properties is shown.     

Effect of surface orientation of CdxHg1−x Te crystals on the properties of surface anodic oxides

Electron spectroscopy for chemical analysis was used to study the effect of surface orientation of Cd_xHg_1?x Te crystals (x=0.19) on the composition of anodic oxide. It is found that anodic oxide compositions on the (111) and (100) crystal surfaces are identical and change gradually from the substrate to the outer surface, whereas the oxide on the (110) surface contains an interlayer of unoxidized Te. This result correlates with some properties known for Cd_xHg_1?x Te oxides.