卷 51, 编号 8 (2017)

The processes of the formation of complex crystal structures–layered crystals of [(Ge, Sn, Pb)(Te, Se)]_m[(Bi, Sb)₂(Te,Se)₃]_n (m, n = 0, 1, 2,…) ternary alloys with different symmetries (space groups R\(\overline 3 \)m, P\(\overline 3 \)m₁, and P2₁/m)—are investigated within the theory of closely packed spheres (CPS theory). The structures of layered binary alloys of the Bi₂Te₃ (R\(\overline 3 \)m) and PbTe (F_m\(\overline 3 \)m and R3m) types are found to be related and formed based on the s3 triplet with cubic symmetry (Fm\(\overline 3 \)m), which is constructed by chalcogen (Se or Te) atoms.

Flash evaporation is used to grow Bi_0.5Sb_1.5Te₃ films 1200 nm thick on mica substrates. The average lateral crystallite sizes in the as-grown films are ~800 nm. The (0001) plane in the crystallites is preferentially parallel to the substrate plane. After heat treatment in an argon atmosphere, the effective lateral size of crystallites in which the third-order axis is perpendicular to the substrate plane increased by a factor of 3–5. The crystallites were preferentially oriented in the substrate plane as well. The thermoelectric-power parameter of Bi_0.5Sb_1.5Te₃ films after their heat treatment in an inert environment increased approximately twofold to values close to that of the corresponding single crystals.

A complex of models for optimizing the design and operation modes of an automotive thermoelectric generator is developed within the proposed approach taking into account the influence of hydraulic resistance of the generator on the internal combustion engine. Several designs of generators for converting the thermal energy of exhaust gases (EGs) of internal combustion engines into electricity due to the Seebeck effect in semiconductor elements, which have different geometries of the continuous-flow part of the generator with different hydraulic resistances, are considered. Models for calculating the thermoelectric elements, gas heat exchanger, and automotive engine are considered jointly. Simulation is performed using the example of a VAZ-21126 engine, which demonstrated that up to 500 W of electric power can be obtained using semiconductor thermoelectric elements based on germanium and lead tellurides.

The temperature and electric- and magnetic-field dependences of the resistivity of the R_0.1Bi_1.9Te₃ compound are investigated. It is shown that, in the low-temperature region, variable-range hopping conductivity is realized in this compound. In the temperature range of hopping conductivity, the electrical resistivity decreases with increasing electric-field strength in the sample, which is typical of charge-carrier tunneling from one localized state in the impurity band to another. Investigation of the transverse magnetoresistance revealed the crossover from the parabolic dependence of the magnetoresistance in low fields to the linear dependence in high fields. The established features of the transport properties of the R_0.1Bi_1.9Te₃ compound are characteristic of inhomogeneous and disordered semiconductors.

A method for measuring the contact resistances of segmented thermoelectric legs is developed. The sensitivity of the method is 2 × 10^–6 Ω cm². The contact resistances of junctions upon switching between different segments of thermoelectric materials are measured. Both junctions and materials of the segments are produced by various methods. The determined contact resistances are in the range of 0.8–3.5 Ω cm². Estimations show that the efficiency loss for a 4-segment leg ~1 cm high at such contact resistances is no more than 5% in the worst case.

The thermoelectric properties of n-type Bi₂Te_2.4Se_0.6 solid solution prepared by the vacuum hot pressing of powder mixtures with different particle sizes are investigated. The powders were prepared by the mechanical grinding of ingots and melt spinning. The microstructure and fracture pattern of a sample cleavage surface are analyzed using scanning electron microscopy and optical microscopy. The thermoelectric characteristics (the Seebeck coefficient, electrical conductivity, and thermal conductivity) are measured at room temperature and in the temperature range of 100–700 K.

A precise method for calculating segmented legs for thermoelectric generators in a one-dimensional approximation by the method of thermal balance with effective values of the thermoelectric parameters is proposed. This method allows one to accurately take into consideration the temperature dependences of the electrical conductivity, the Seebeck coefficient, and thermal conductivity. The effect of contact resistance on the resulting power-conversion efficiency is also taken into account. The procedure of segmented leg calculation is demonstrated, and a method of transitioning from leg calculation to thermoelement calculation is proposed.

The superconducting properties of Pb_0.05Sn_0.95Te semiconductor alloy doped with 5 at % of In are investigated at a hydrostatic pressure of P < 7 kbar. At increasing pressure P > 1.35 kbar and T ≥ 1.3 K, the resistivity step to ρ = 0 in the temperature and magnetic-field dependences ρ(T) and ρ(H), which corresponds to the transition to the superconducting state, disappears. The experimental results are indicative of a decrease in the density of states at the Fermi level with increasing pressure, which can be interpreted as an indium-level shift deep into the valence band. The obtained data refine and supplement the results of studies devoted to investigation of the baric dependences of the critical parameters of the superconducting transition in (Pb_zSn_1–z)_0.95In_0.05Te with varying lead content z.

The results of studying the thermoelectric properties of p-type Bi_0.5Sb_1.5Te₃ alloy samples prepared by melt spinning quenching are presented. The material after melt spinning is shaped as thin ribbons and has a quasi-amorphous structure. The thermoelectric properties (thermoelectric power and electrical resistance) and crystallization processes of as-prepared melt-spun ribbons are studied at 300–800 K for the first time. The stability range of the initial state, the crystallization-onset temperature, and the effect of thermal annealing on the thermoelectric-power factor of the alloy are determined.

Mn_0.1Ag_0.9In_4.7S_7.6 single crystals are for the first time grown by the Bridgman method (vertical variant). The single crystals crystallize in the cubic spinel structure. The band gap of the single crystals is determined from the transmittance spectra in the region of the fundamental absorption edge at temperatures of T = 295 and 80 K. Thermal expansion is studied by the dilatometric method in the temperature range 80–500 K. The coefficients of thermal expansion, the Debye temperatures, and the rms (root mean square) dynamic displacements of atoms are calculated.

Using an improved parameterless unified Argand diagram method, the permittivity spectra of InAs and InSb crystals in the range of 15–40 eV are decomposed into thirteen and twelve separate components, respectively, with the three main parameters, specifically, the maximum energies, half-width, and oscillator strength determined for each of them. The oscillator strengths are in the ranges of 0.006–0.10 for InAs and 0.014–0.076 for InSb. The permittivity spectra were preliminary calculated on the basis of experimental reflectance and absorption spectra using Kramers–Kronig integral relations. On the basis of a model of interband and exciton transitions, the nature of the obtained transition bands is suggested.

The effects of 8-MeV proton irradiation on n-3C-SiC epitaxial layers grown by sublimation on semi-insulating 4H-SiC substrates are studied. Changes in the sample parameters were recorded by the Hall-effect method and judged from photoluminescence spectra. The Hall method was employed to distinguish between the effects of irradiation on the charge-carrier concentration and mobility. It is found that the charge-carrier removal rate (V_d) is ~110 cm^–1. Full compensation of the samples with an initial charge-carrier concentration of ~6.5 × 10¹⁷ cm^–3 is observed at irradiation doses of ~6 × 1015 cm^–2. It is found that the mobility at these doses decreased by only a factor of 2.5. Compared with 4H and 6H silicon carbide, no significant increase in the intensity of so-called defect-related photoluminescence is observed.

The infrared optical properties of anisotropic mesoporous silicon films containing free charge carriers (holes) are studied experimentally and theoretically. The results of simulation of the optical properties of the produced samples in the effective-medium approximation show a heavy dependence of the birefringence, reflection anisotropy, and dichroism on the concentration of free charge carriers. The unsteady behavior of the differential transmittance recorded for the samples at mutually perpendicular polarization directions of light are attributed to the effect of charge carriers with a concentration on the order of 10¹⁹ cm^–3. The results of the study suggest that anisotropic silicon nanostructures are promising materials for infrared photonics and terahertz engineering.

The composition of the thin layer of a plane-parallel solid-state structure affects the propagation of differential charge carriers fluxes in the thickness of the layer and through it. Scattering of these fluxes at the boundaries of the thin layer affects also the distribution function of charge carriers. This scattering is correctly taken into account in integrated boundary conditions for the kinetic equation. For a plane-parallel layer, the kinetic equation (in the approximation of the relaxation time) is reduced to a convenient form, which describes the propagation of differential fluxes in the thickness of the layer. The solution for thick and thin layers of different types (metal, insulator, semiconductor) is analyzed. Practically important problems, in which the obtained solutions can be effectively used, are specified.

The results of studying the growth of filamentous Ge structures in aqueous electrolytes at various temperatures using In and Sn nanoparticle arrays as nucleation sites are given. The temperature of Ge cathodic deposition process from aqueous solutions has a significant effect on the layer structure deposited onto the surface. In the presence of metal particles in the molten state, filamentous Ge structures grow due to the cathodic reduction of Ge-containing ions on the electrode surface, followed by dissolution and crystallization in the melt at the substrate interface. The results obtained show the crucial role of liquid metal particles during the electrochemical formation of germanium nanowires.

The structural, chemical, and electronic properties of epitaxial graphene films grown by thermal decomposition of the Si-face of a semi-insulating 6H-SiC substrate in an argon environment are studied by Raman spectroscopy, atomic-force microscopy, the low-energy electron diffraction method, X-ray photoelectron spectroscopy, angle-resolved photoemission spectroscopy and X-ray absorption spectroscopy at the carbon K edge. It is shown that the results of a systematic integrated study make it possible to optimize the growth parameters and develop a reliable technology for the growth of high-quality single-layer graphene films with a small fraction of bilayer graphene inclusions.

An analytical expression is derived for the current–voltage characteristic of a Schottky diode at a high injection level of minority carriers. It is shown that, even at very high current densities, the higher the base doping level, the larger the voltage drop across the diode. The physical mechanism responsible for this “paradoxical” result is analyzed. The validity of the analytical result is confirmed by a numerical calculation with software that takes into account the whole set of nonlinear effects caused by a high injection level in the base layer and by heavy doping of the emitter region.

The properties of epitaxial Ga_xIn_1–xP alloys with an ordered arrangement of atoms in the crystal lattice are studied by a number of structural and microscopic methods. The alloys are grown by metal-organic chemical vapor deposition onto single-crystal GaAs(100) substrates. It is shown that, under conditions for the coherent growth of an ordered Ga_xIn_1–xP alloy on a GaAs(100) substrate, atomic ordering results in radical modifications of the structural properties of the semiconductor compared to the properties of disordered alloys. Among these modifications are a change in the crystal-lattice parameter and, as a consequence, lowering of the crystal symmetry and the formation of two different types of surface nanorelief. With consideration for elastic strains, the parameters of Ga_xIn_1–xP alloys with ordering as functions of the order parameter are calculated for the first time. It is shown that all experimental data are in good agreement with the developed theoretical concepts.

Indium-antimonide quantum dots are for the first time formed on the surface of an epitaxial In_0.25GaAsSb layer isoperiodic to a GaSb(001) substrate by liquid-phase epitaxy in the range of temperatures T = 450–467°C. Transmission electron microscopy shows that, the shape of quantum dots is close to a truncated cone and their distribution in terms of height and base size in the ensemble is monomodal. Large-sized quantum dots (with a base size of 30–50 nm and height of 3 nm) exhibit specific contrast in the plane-view diffraction-mode image, which is indicative of the presence of misfit defects. Modification of the chemical composition of the working surface of the substrate by the deposition of an epitaxial In_0.25GaAsSb layer makes possible a threefold increase in the density of the ensemble of InSb quantum dots (1 × 10¹⁰ cm^–2) compared to the density in the case of deposition directly onto the GaSb binary compound.

The name of the last author should read J. E. Batler.