Vol 53, No 8 (2019)

By means of Rutherford backscattering spectrometry, electron microscopy, and energy-dispersive X-ray spectroscopy, the distribution and interaction of In and As atoms implanted into thermally grown SiO₂ films to concentrations of about 1.5 at % are studied in relation to the temperature of subsequent annealing in nitrogen vapors in the range of T = 800–1100°C. It is found that annealing at T = 800–900°C results in the segregation of As atoms at a depth corresponding to the As⁺-ion range and in the formation of As nanoclusters that serve as sinks for In atoms. An increase in the annealing temperature to 1100°C yields the segregation of In atoms at the surface of SiO₂ with the simultaneous enhanced diffusion of As atoms. The corresponding diffusion coefficient is D_As = 3.2 × 10^–14 cm² s^–1.

A version of the spin–orbit interaction of orbitally moving and spin-oriented electrons in a longitudinal autosoliton in indium antimonide under a longitudinal magnetic field is proposed and considered. The additional energy gained by spin–orbit electrons due to this interaction is determined. Expressions for the change in the mobility during the orbital motion of electrons under a magnetic field and the additive mobility of spin-oriented electrons are derived and calculated. The coefficients of the mutual influence of changing electron mobility in the case of orbital motion and the additive mobility of spin-oriented electrons are calculated.

Solid solutions of cadmium in niobium and NbCd₂ phase are formed by magnetron sputtering and coprecipitation on substrates moving relative to the flow of Nb and Cd particles. The NbCd₂ phase can be described by a tetragonal unit cell with the parameters a = 0.84357 nm, c = 0.54514 nm, and c/a = 0.6426. A very high hole concentration in NbCd₂ is established by studying the coating absorption and transmission spectra corresponding to the intermetallic-compound composition near the fundamental absorption edge, determining the band gap, and measuring the carrier mobility. Such a concentration is characteristic of a strongly degenerate semiconductor or metal. The band gap is determined to be 1.26 eV. The variation in the concentration of carriers and their mobility depending on the cadmium concentration in coatings of the Nb–Cd system confirms the occurrence of the NbCd₂ phase.

The influence of a SiO₂ layer deposited onto nanostructured transparent conductive films of indium and tin oxide (ITO) on their optical characteristics is investigated. For this purpose, SiO₂ films of various thicknesses are deposited by magnetron sputtering on samples with ITO films containing whiskers of preferentially vertical orientation and possessing steadily decreasing reflectance. It is shown that this makes it possible to attain noticeable coating antireflection under the condition of the uniform overgrowth of ITO whiskers by the SiO₂ layer. The influence of the SiO₂ layer on the optical characteristics of a dense unstructured ITO film is also investigated. The results for structured and unstructured ITO/SiO₂ coatings with identical material mass contents are compared. It is noted that due to the liability of ITO material to degradation during operation in the composition of transparent conductive contacts, the results can also be interesting for the formation of coatings more resistant to the effect of the environment.

Tunneling and magnetic tunneling are investigated in graphene/h-BN/graphene van der Waals heterosystems. Two new types of systems are found, in which negative differential conductivity regions are implemented due to resonant tunneling through defect levels in the h-BN barrier, and current caused by their presence is generated.

Monodisperse spherical nanoporous silicon (np-Si) particles of submicrometer size are fabricated with mesoporous silica particles as a template. Silicon is synthesized within the mesopores of monodisperse silica particles by the thermal decomposition of monosilane. Then, the template material (a-SiO₂) is removed by wet etching. The particles obtained have a small root-mean-square size scatter (no more than 10%) and large specific surface area (250 m² g^–1) and pore volume (0.5 cm³ g^–1). It is shown that np-Si particles exhibit photoluminescence in the visible and near-IR (infrared) spectral ranges.

The influence of the length of ZnO nanorods (500 nm in diameter) on the mode structure and spontaneous luminescence in the ultraviolet spectral region is studied by optical luminescence microscopy. It is shown that individual nanorods with a metal mirror on one face exhibit only two or three laser modes in the case of short nanocavity lengths (8–30 μm). Different values of the optical losses of the longitudinal and transverse waveguide modes are established for a ZnO nanorod lying on a glassy substrate. The quadratic dependence of the spontaneous luminescence intensity on the rod length can be attributed to improvement of the optical quality factor Q of bound longitudinal modes of light within longer rods (the Purcell effect).

The effect of thermal annealing on the photovoltaic properties of a GaP/Si heterostructures obtained by plasma-enhanced atomic layer deposition under different conditions is examined. It is shown that in the structures containing amorphous GaP, annealing at 550°C leads to a sharp decrease in the quantum efficiency and open-circuit voltage, while in the structures with microcrystalline GaP on an epitaxial sublayer, the photovoltaic characteristics are improved. Annealing at a temperature of 750°C improves the photovoltaic characteristics in all the structures due to the diffusion of phosphorus atoms from GaP to Si and leads to the formation of a layer with n-type conductivity in the substrate. As the annealing temperature is increased to 900°C, the carrier lifetime in the silicon substrate decreases. It is shown that the atomic-layer-deposition technique is promising for the formation of a GaP nucleation layer on the surface of silicon before subsequent epitaxial growth.

Quantum dots of the group of wide-gap and narrow-gap semiconductors are synthesized and investigated under identical conditions, which makes it possible to perform the comparative analysis and modeling of the mechanisms of radiative recombination and luminescence, for which a stable exciton bond between the electron and hole has an important role. Exciton states are unstable for quantum dots without a shell and narrow-gap semiconductors, which leads to a substantial decrease in the probability of radiative recombination and, correspondingly, the quantum yield of luminescence. The experimental values of the spectral position of the luminescence maximum for quantum dots with clear manifestation of the exciton recombination mechanism noticeably shift to the long-wavelength region with respect to the calculated ones. In calculations and analysis, we use the effective electron mass for bulk semiconductors. The observed good correspondence of the calculated values of the maximum and spectral band with the experiment can mean that quantum dots have a long-range order crystalline structure similar to that one observed in single crystals and polycrystals.

The relaxation and thermal processes and interphase phenomena in composites based on ferroelectrics and a polymer matrix are studied. It is shown that the charge stabilized at the interface of the composite during its electrothermopolarization is mainly determined by the structure of the polymer matrix and the piezoelectric phase. The results obtained make it possible to reveal the main factors affecting the piezoelectric properties of the heterogeneous polymer–ferroelectric ceramic system. Polyolefins and fluorine-containing polar polymers are used as the organic phase, and ferroelectric ceramics of rhombohedral, tetragonal, and mixed structures serve as the inorganic phase. The relaxation processes and interphase phenomena are studied using a differential scanning calorimeter, and the charge state is analyzed by recording the thermally stimulated depolarization current. The charge-state stability is determined by the electret potential difference of the composites. The molecular relaxation is analyzed by the dielectric method. It is established that the composites in which the interphase interaction is more pronounced are characterized by high piezoelectric properties.

Microdisk lasers 10–30 μm in diameter operating at room temperature without thermal stabilization and with an active region based on nanostructures of hybrid dimensionality—quantum wells–dots—are investigated. High-frequency measurements of the microlaser response are performed in the direct small-signal modulation mode, which makes it possible to establish the parameters of the operating speed and analyze their dependence on the microlaser diameter. It is found that the K factor is (0.8 ± 0.2) ns, which corresponds to optical losses of ~6 cm^–1, and no regular dependence on the diameter is observed. It is found that the low-frequency component of the damping coefficient of relaxation oscillations is inversely proportional to the diameter. This character of the dependence evidences a decrease in the carrier lifetime in small-diameter microcavities, which can be associated with the prevalence of nonradiative recombination on their side walls.

The results of a study and the development of a module designed for energy transmission via atmospheric channels are presented. The four-cell module based on single-junction metamorphic InGaAs/GaAs converters grown by metal-organic vapor-phase epitaxy has an open-circuit voltage of ~3 V. It is shown that the monochromatic efficiency (at a wavelength of 1064 nm) of this module is 31.5% under exposure to a Xe-lamp with a radiation power of 1.5 W/cm².

The possibility of synthesizing integrated GaN/por-Si heterostructures by plasma-assisted molecular beam epitaxy without an A1N/Si buffer layer is demonstrated. The beneficial effect of the high-temperature nitridation of a silicon substrate before GaN growth on the crystal quality of the GaN/Si layers is shown. It is established that, to obtain two-dimensional GaN layers on Si(111), it is reasonable to use compliant por-Si substrates and low-temperature GaN seed layers with a 3D morphology synthesized by plasma-assisted molecular beam epitaxy at relatively low substrate temperatures under stoichiometric conditions and upon enrichment with nitrogen. In this case, a self-assembled array of GaN seed nanocolumns with a fairly uniform diameter distribution forms on the por-Si substrate surface. The basic GaN layers, in turn, should be grown at a high temperature under stoichiometric conditions upon enrichment with gallium, upon which the coalescence of nucleated GaN nanocolumns and growth of a continuous two-dimensional GaN layer are observed. The use of compliant Si substrates is a relevant approach for forming GaN-based semiconductor device heterostructures by plasma-assisted molecular beam epitaxy.

The mode of the growth of InGaAs quantum dots by MOS-hydride epitaxy on GaAs substrates without a deviation and with a deviation of 2° is selected for laser structures emitting at wavelengths above 1.2 μm at room temperature. As a result, a quantum-dot density of 4 × 10¹⁰ cm^–2 is achieved. Stimulated emission is observed in laser structures with seven layers of quantum dots at a wavelength of 1.06 μm at liquid-nitrogen temperature. The threshold power density of optical pumping is about 5 kW/cm².