卷 53, 编号 7 (2019)

In southern countries, including European states, solar collectors for additional water-heating systems are widely used. However, the disadvantage of such systems is that a considerable proportion of solar energy cannot be used with increasing water temperature and dissipates into the environment. It is proposed to use waste heat at a high temperature, which is supplied to a thermoelectric generator (TEG) operating on the basis of a temperature difference between the hot water in the solar collector and cold water supplied to a radiator on the other TEG side. This is a new application of thermoelectric converters, in which the converter can act not only as a source of electrical energy but also as a source of low-potential heat coming from the radiator. The total conversion efficiency in such devices can reach 90%. It is shown that the use of p-type legs in a TEG with the cleavage planes of the legs parallel to the heat-flux direction instead of the conventional parallel orientation results in an increase in the thermoelectric efficiency by 25% on average in the temperature range of 100–300°C.

A patented thermoelectric intensifier of heat transfer between two moving media with different temperatures is investigated. Its design envisages the use of fan units in order to increase the heat-transfer intensity between media. A mathematical model of the device is developed based on solution of the heat balance equation for media flows in transport zones under conditions of forward flow. The calculated data are presented in the form of a dependence of the temperature change of moving media along the intensifier for different values of the heat-transfer coefficient between the thermoelectric cell junctions and the air medium in the device gap. It is established that, the larger the temperature difference between the inlet media, the sharper the dependence of the thermopile limit on the heat-transfer coefficient.

The field and temperature dependences of the electrical conductivity of europium sulfide are studied in the temperature range 160–430 K. It is found that the electrical conductivity increases in strong electric fields of up to 2 × 10⁴ V/cm by the Poole–Frenkel mechanism.

The influence of rapid thermal annealing on the electrical and radiative properties of Ge:Sb/Si(001) epitaxial layers with an antimony concentration substantially higher than its equilibrium solubility in germanium is investigated. Local variations in the electrical and luminescence properties of n-Ge/Si(001) throughout the structure depth are investigated by means of the precise chemical etching of Ge. It is shown that a variation in the properties of such layers at relatively low (≤500°C) annealing temperatures (decrease in the electron concentration and photoluminescence intensity) occur in the absence of the noticeable diffusion-related redistribution of dopant atoms. Variations in the electrical and luminescence properties of Ge:Sb layers at relatively high (≥700°C) annealing temperatures are caused by the substantial redistribution of Sb due to its bulk diffusion and desorption from the surface. In particular, Sb diffusion leads to the formation of doped layers in initially undoped parts of the studied structures, which start to give a substantial contribution to the resulting conductivity of the structure and its photoluminescence signal.

The effect of growth conditions on the structural perfection of AlInGaAsP/InP thin-film heterostructures is discussed. The key parameters determining the structural perfection and surface quality of thin AlInGaAsP epitaxial films grown on indium-phosphide substrates from the liquid phase in a temperature-gradient field are determined.

Spherical distributed Bragg reflectors (SDBR) for near-IR (infrared) applications are fabricated by plasma-enhanced chemical-vapor deposition. The SDBRs consist of alternating quarter-wave layers of amorphous hydrogenated silicon (a-Si:H) and amorphous silicon oxide (a-SiO₂), deposited onto a glass or quartz microsphere that has a diameter of 500 μm and is doped with erbium ions. The reflection and transmission spectra of a SDBR are measured at different points on its surface. A wide band with high reflectance and low transmittance, i.e., a stop band, is detected. It is demonstrated that, for different radial directions from the center of the microspheres, the stop bands overlap to form an omnidirectional stop band. The influence exerted by the omnidirectional stop band on the spontaneous emission of erbium ions (1.53 μm) from the quartz microsphere is studied. It is shown that the omnidirectional stop band suppresses the intensity of spontaneous emission by more than an order of magnitude.

The electrical and galvanomagnetic properties of unrelaxed heteroepitaxial InAs_{1 –x}Sb_x structures (x = 0.43 and 0.38) in a wide temperature range of 5–300 K and magnetic fields up to 8 T are studied. From the thermal-activation dependence of the electrical conductivity, the band gap of the composition InAs_0.57Sb_0.43 is estimated as 120 meV. The electron concentration in InAs_{1 –x}Sb_x (6 × 10¹⁶ cm^–3 for InAs_0.62Sb_0.38 and 5 × 10¹⁶ cm^–3 for InAs_0.57Sb_0.43) determined from the Hall effect agrees well with the electron concentration calculated from the Shubnikov–de-Haas oscillations. We also carry out the spectral ellipsometric studies of unrelaxed heteroepitaxial structures of InAs_{1 –x}Sb_x (x = 0.43 and 0.38) in the photon energy range of 1–6 eV. The spectral dependences of the imaginary and real parts of the dielectric constant are determined. The dispersion dependences of the refractive index and the extinction coefficient are calculated and presented.

The temperature dependences of the Hall coefficient and magnetoresistivity of a p-type HgTe/CdHgTe double quantum well with HgTe layers of critical thickness in the temperature range T = 35–300 K under magnetic fields up to 9 T are investigated. The position of the earlier observed reentrant quantum Hall transition from plateau i = 1 to plateau i = 2 is found to be close to the transition field from light to heavy holes with an increase in the magnetic field in the classical Hall effect. It is found that thermally activated light electrons contribute to the Hall effect along with light and heavy holes at T ≥ 35 K. The activation energy of electrons is estimated from the temperature dependence of the electron concentration as 28 meV, which exceeds the calculated value from the lateral maximum of the valence subband to the edge of the lowest conduction subband, probably because of heterostructure asymmetry.

The longitudinal and Hall components of the resistivity tensor are measured in structures with multiple HgTe layers 16 nm thick in magnetic fields to 12 T at temperatures from 1.5 to 300 K. The slope of the magnetic-field dependence of the Hall resistance is found to change its sign at a certain critical temperature T_c = 5 and 10 K in the two studied samples, which indicates the presence of two types of charge carriers and a change in the relation between their contributions to the Hall resistance with temperature. The low critical temperature and manifestation of the “two-component” nature of the Hall curves only at T > T_c prove that the ground state of the system at T = T_c is gapless. At higher temperatures (20 K < T < 200 K), the Hall concentration is proportional to the temperature with good accuracy. The description of the charge-carrier dispersion laws by the 8-band kp model taking into account Γ₈-band-edge splitting caused by mechanical stresses, which forms both types of state in HgTe, makes it possible to quantitatively describe the observed magnetotransport features. It is shown that they are associated with the simultaneous filling of electron and hole states formed as a result of mixing interface states responsible for the topological-insulator phase and the quantum-confined states in the Γ₈ band.

An investigation into carrier-transport mechanisms in mesoporous silicon layers for the cases of transport along the layer surface (perpendicularly to silicon columns) and perpendicularly to the layer surface (along silicon columns) is presented. It is established that the conductivity measured along the layer surface is much lower than the conductivity measured perpendicularly to the surface. It is concluded from analysis of the temperature and frequency dependences of the conductivity that the carrier-transport mechanisms are different in the cases under consideration (along and perpendicularly to the surface).

The orientation relationships between the low-temperature monoclinic semiconductor acanthite α-Ag₂S and the high-temperature body-centered argentite β-Ag₂S are determined based on high-temperature X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) data on silver sulfide. It is found that, in contrast to acanthite, the possible distances between silver atoms in cubic argentite are too small to allow Ag atoms to occupy metal sublattice sites with a probability of 1. It is shown that the (010) and (001) atomic planes of acanthite are parallel to the (1\(\bar {1}\)0) and (221) planes of argentite, respectively. The found orientation relationships between acanthite and argentite are important for understanding the physical operation of the Ag₂S/Ag heteronanostructure, which is considered as a potential basis for designing resistive switches and nonvolatile memory devices.

The Green’s function method in the tight-binding approximation is used to obtain analytical expressions for the electronic spectra and densities of states for two carbyne structural modifications (cumulene and polyyne). Metal and semiconductor substrates are considered and charge-transfer estimates are deduced. Criteria for the occurrence of a charge-density wave in free-standing and epitaxial carbynes are proposed taking into account the intra- and interatomic Coulomb repulsion. Analytical expressions for the phonon spectrum of free-standing carbyne are presented. The data obtained are compared with the results of numerical calculations performed by other researchers.

The operation of diffused step recovery diodes (dSRDs) as current interrupters in high-power nanosecond pulse generators is studied in detail for the first time by numerical computer simulation. One of the necessary conditions for minimizing the loss in dSRDs is specified. The dependences of the prepulse voltage, front duration, amplitude and duration of the pulse formed on a resistive load, and the switching-loss energy in a dSRD on the device area and break current density are obtained. It is shown that the simulation results can be described by simple analytical formulas obtained in the second part of the work with an error of 10–20% if the pulse amplitude does not exceed the dSRD avalanche breakdown voltage. A generalized figure of merit of dSRDs is proposed, which can be used to optimize the dSRD parameters and operation mode and compare the efficiency of current interrupters of different types.

The effect of low-temperature (up to 600°C) isothermal and isochronous annealing on the electrical characteristics of irradiated n-4H-SiC JBS Schottky diodes is studied. Irradiation is performed with 0.9-MeV electrons at a dose of 1 × 10¹⁶ cm^–2. It is shown that the forward current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the irradiated diodes are mainly restored at annealing temperatures of up to 300°C. As the annealing temperature is raised to 500°C, nearly 90% of the defects introduced by irradiation with fast electrons are annealed out. The possible recommended mode of stabilizing annealing to be used in radiation-defect engineering (RDE) is 500°C, 30 min.

Data on the dependence of the growth rate of Si layers deposited onto Ge(111) by the hydride method on their thickness at the initial heteroepitaxy stage are reported. The effect of a Ge substrate within ten grown silicon single layers on the Si-film growth rate is demonstrated. Based on the data obtained, the kinetic coefficients responsible for the rate of the main physicochemical processes related to the interaction of hydride molecular beams with the growth surface are calculated. An analysis of the capture probability and rates of pyrolysis of the adsorbed Si(Ge) hydride molecules on the pure Ge(Si) surfaces reveals the dependence of their behavior on the growing-layer thickness. Comparison of the results obtained during Si-layer growth on Ge shows that the pure germanium surface has higher adsorption and catalytic abilities with respect to silane molecules than the pure Si surface. The unstrained pure Si surface has higher adsorption and catalytic characteristics with respect to Ge-hydride molecules.

The influence of using a buffer sublayer of nanoporous por-Si on the morphological, physical, and structural properties of nanocolumnar In_xGa_{1 –x}N structures fabricated by plasma-activated molecular-beam epitaxy on single-crystal Si(111) substrates is shown. Using a set of structural-spectroscopic analytical methods, the electronic structure of the grown heterostructures, morphology, and optical properties are investigated, and the interrelations between them are established. It is shown that the use of a por-Si sublayer makes it possible to attain a more uniform distribution of diameters of In_xGa_{1 –x}N nanocolumns and to increase the photoluminescence intensity of the latter.