Vol 53, No 9 (2019)

A double-mirror two-dimensional Bragg resonator design based on structures of planar geometry, which is typical of both band-to-band and quantum-cascade heterolasers, is suggested. The distinguishing feature of this design is the coupling between longitudinal and transverse energy flows in two-dimensional Bragg mirrors. The eigenmode spectrum of the structure is described. It is shown that the proposed design can be used for synchronizing radiation emitted in lasers and laser arrays.

The results of investigation of thermoelectric materials fabricated by spark plasma sintering and based on Si_{1 –x}Ge_x solid solutions doped with Sb to a concentration of 0–5 at % are presented. It was found that, at Sb concentration below 1 at %, efficient doping of the solid solution was carried out during the sintering process, which allowed us to form a thermoelectric material with a relatively high thermoelectric figure of merit. An increase in the concentration of antimony in the range of 1–5 at % led to a change in the mechanism of doping, which resulted in an increase in the resistance of materials and the segregation of Sb into large clusters. For such materials, a significant decrease in the Seebeck coefficient and thermoelectric figure of merit was noted. The highest obtained thermoelectric figure of merit (ZT) with Sb doping was 0.32 at 350°C, which is comparable with known analogues for the Ge_xSi_{1 –x} solid solution.

Mechanisms of the suppression of the electron-hole exchange interaction in nonradiative excitons with a large in-plane wave vector in high-quality heterostructures with quantum wells are analyzed theoretically. It is shown that the dominant suppression mechanism is exciton-exciton scattering accompanied by the mutual spin flips of like carriers (either two electrons or two holes), comprising the excitons. As a result, the electron spin polarization in nonradiative excitons may be retained for a long time. The analysis of experimental data shows that this relaxation time can exceed one nanosecond. This long-term and optically controllable spin memory in an exciton reservoir may be of interest for future information technologies.

The features of transient processes under the field effect in PbSnTe:In films with a variation in the current up to a factor of 10⁵ are studied at helium temperatures. These features qualitatively correspond to a model, in which a high concentration of traps with different parameters is present on the PbSnTe:In surface. The role of the surface is confirmed by a strong variation in the experimental characteristic after the chemical removal of native oxides from the PbSnTe:In surface and its passivation by an Al₂O₃ layer.

A comparison of the features of electron transport in diodes based on 6-, 18-, 30-, 70-, and 120-period GaAs/AlAs superlattices with a similar design is performed. However, the number of periods and diode areas are different. The values of the parasitic resistances of the near-contact diode regions are correlated, and the specific voltage drop across one superlattice period is determined for all special points in the current–voltage characteristics of the diodes. The mechanism of the appearance of stable current oscillations in diodes based on 6-, 18-, 30-, 70-, and 120-period GaAs/AlAs superlattices with a high doping level is investigated.

The plasma-chemical deposition of diamond-like carbon (DLC) films onto heavily boron-doped single-crystal p-type diamond (the concentration ~10²⁰ cm^–3) in CH₄ + Ar plasma is conducted. The deposition rate is 7 nm min^–1. The elemental composition and properties of the films are studied in detail. It is found that the films are enriched with hydrogen, possess a density of 2.4 g cm^–3, and exhibit an ultrasmooth surface (with a roughness of 0.4 ± 0.2 nm).

The spectrum of amplification of terahertz radiation in a structured active graphene bilayer consisting of two identical periodic graphene microribbon arrays separated by a thin dielectric barrier layer is theoretically investigated. The system supports optical and acoustic plasmon modes. The resonant frequencies of the optical and acoustic modes change oppositely with the dielectric-layer thickness, which allows plasmon-mode anticrossing. It is shown that the investigated graphene structure is characterized by a strong plasmon response and giant terahertz-radiation amplification at plasma resonance frequencies in the vicinity of the anticrossing between the optical and acoustic plasmon modes at room temperature.

The simulation of reversible single events in test samples of static memory microcircuits with design norms of 0.5, 0.35, 0.25, and 0.1 μm under the effect of neutron fluxes with various energies is performed. It is shown theoretically and experimentally that reversible single events can occur in modern microelectronics and nanoelectronics products under the effect of a fission-spectrum neutron flux caused by the passage of primary recoil atoms and nuclear reaction products along the microcircuit surface perpendicularly to the electric current lines in the near-drain transistor area. A series of irradiation experiments of static memory circuits with design norms of 0.35 μm is interpreted based on the proposed model.

The results of experiments aimed at the observation of split 1s states in Mg-doped Si are reported. From the results, it is possible to determine the chemical shift and exchange interaction energy of a neutral Mg donor in Si. The position of the 1s(E), 1s(T₂), and 2s(A₁) parastates determines the possibility for attaining population inversion and the specific mechanism of stimulated Raman scattering. The energy of the 1s(T₂) parastate is determined from the position of the Fano resonances in the photoconductivity spectrum of Si:Mg at T = 4 K, and the energies of the 1s(T₂) and 1s(E) orthostates from the transmittance spectra at elevated temperatures. On the basis of the experimental data, the relaxation rates are estimated, and the possible mechanisms of stimulated emission are analyzed.

A GaAs/AlAs/GaAs/AlAs/Ge heterostructure grown on a Si/Al₂O₃(1\(\bar {1}\)02) substrate is formed and studied. The Ge buffer layer is produced by the “hot wire” technique, whereas the III–V layers are grown by metal–organic vapor-phase epitaxy. The optical quality of the III–V layers is determined by photoluminescence spectroscopy. Structural studies are performed by high-resolution transmission electron microscopy. The elemental composition is determined by energy-dispersive X-ray spectroscopy. In the study, the possibility of growing a single-crystal GaAs layer on a Si/Al₂O₃ substrate through AlAs/GaAs/AlAs/Ge buffer layers is shown.

The formation of a disordered defect region in bulk silicon is simulated using the molecular-dynamics method for various energies of a primary recoil atom. Variations in the volume and number of radiation-induced defects in a cluster during its formation are calculated. The generation rates of nonequilibrium carriers and amplitude-temporal dependences of pulses of ionization currents in test Schottky diodes with hyperhigh frequencies are found theoretically.

A composite nanostructure based on quasi-one-dimensional InP nanowires with an InAsP nanoinsert, grown on a Si(111) substrate by the method of molecular-beam epitaxy, and CdSe/ZnS zero-dimensional colloidal quantum dots is reported for the first time. The nonradiative resonance energy transfer between components of the hybrid nanostructure, namely, between the colloidal quantum dots and the nanoinsert, is experimentally confirmed.

The photoconductivity spectra of epitaxial CdHgTe films are investigated by Fourier-transform spectroscopy at various temperatures. Features associated with both the interband absorption and ionization of impurity/defect states are found in the spectra. Their evolution with temperature is traced. The temperatures of “vanishing” of the impurity features are determined, which makes it possible to assess the acceptor concentration in the structures under study using the electroneutrality equation.