Vol 51, No 10 (2017)

A phenomenological model of double acceptors formed by Cu, Ag, and Au atoms in GaAs is presented. Experimentally observed phenomena related to the specific features of the spatial and electronic structure of these centers (the suppression of the Jahn–Teller effect by uniaxial pressure, softening of the crystal, recombination-induced reorientation of Jahn–Teller distortions of the center, the decrease in the stationary degree of alignment of center distortions by uniaxial pressure with an increase in the recombination rate of nonequilibrium electron–hole pairs through the center, the relaxation absorption of ultrasound, etc.) are described.

The phenomena occurring at the local pulsed photoexcitation of intrinsic nonequilibrium highconcentration charge carriers in silicon are experimentally investigated. The effect of a substantial increase in the lifetime of photoexcited charge carriers is found. It is shown that the effect of a substantial increase in the lifetime of charge carriers is caused by a change in the degree of degeneracy and displacement of the impurityrecombination level towards the Fermi level due to local thermoelastic deformation of the crystal and the corresponding distribution of the concentration of nonequilibrium charge carriers.

The reflectance spectra of a p-Bi₂Te₃:Sn crystal are recorded in the range 50–7900 cm^–1. The spectra possess features characteristic of charge-carrier plasma oscillations and a contribution of phonons. It is shown that the dielectric function that is used in the context of Drude–Lorentz theory and includes the contributions of hole plasma oscillations and two phonons adequately describes the experimental data obtained at room temperature and at a temperature of T = 78 K.

The interaction of magnetron-sputtered metal iron with titanium-oxide films upon isothermal vacuum annealing is studied by X-ray phase analysis, secondary-ion mass spectrometry, atomic-force microscopy, and mathematical simulation. A mechanism for the formation of complex oxides at grain boundaries is suggested. The mechanism is based on the reaction diffusion of metal iron into titanium oxide. A quantitative model of reaction interdiffusion in two-layer polycrystalline metal–oxide film systems with limited component solubility is developed. From numerical analysis of the experimental distributions of the metal concentrations in the Fe–TiO₂ film system, the individual diffusion coefficients are determined. It is found that, under the conditions of vacuum annealing at 1073 K, the diffusion coefficients of iron and titanium are 8.0 × 10^–13 and 3.0 × 10^–15 cm² s^–1, respectively.

The mechanism of resistive switching in films of partially fluorinated graphene is investigated. The films are obtained on the basis of a number of graphene suspensions with different composition and various degree of fluorination. The dependence of the value of resistive switching on the presence of organic additives (N-methylpyrrolidone and dimethylformamide) in the suspension composition and the degree of fluorination are found experimentally. It is shown that, for films obtained from a suspension without organic components, no resistive switching is observed independently of the degree of fluorination. The most profound effect of ~10–20 times is found for films containing dimethylformamide. A physical model for the films is proposed; according to this model, the dependence under observation is related to the presence of encapsulated functional groups formed from dimethylformamide molecules manifesting electrical activity in the investigated films. The measured current–voltage characteristics of the films are described in the best way by the Frenkel–Poole model with an activation energy of 0.08 eV of centers responsible for conduction. The value of switching depends on the degree of fluorination of the initial suspensions. The greatest effect is observed at a degree of fluorination of the suspensions of ~CF_0.25. Suspensions of partially fluorinated graphene investigated in this study are suitable for fabricating device structures by the 2D-printing technology.

The localization behavior of a two-dimensional electron gas confined at the surface of a heavily doped semiconductor under conditions of the “natural” size effect in the space-charge region is investigated. The scattering of low-energy electrons by the chaotic potential formed at the surface by point charges of ionized impurities is analyzed and the electron mean free path is determined. A criterion for strong localization in this two-dimensional electron system is obtained on the basis of the Ioffe–Regel criterion.

We report on a study of lasers with an emission wavelength of about 1.5 μm and high temperature stability, synthesized on an InP (001) substrate. Self-organized InAs quantum dots capped with a thin GaAs layer are used as the active region of the laser. A quaternary InGaAsP solid solution with a band-gap width of 1.15 eV serves as the waveguide/matrix layer. A high characteristic temperature of the threshold current, T₀ = 205 K, is reached in the temperature range 20–50°C in ridge-waveguide laser diodes. A correlation between the values of T₀ and the band-gap width of the waveguide layers is found.

Vertical transport in type-II heterojunctions with a two-barrier AlSb/InAs/GaSb/AlSb quantum well (QW) grown by MOVPE on an n-InAs (100) substrate is investigated in quantizing magnetic fields up to B = 14 T at low temperatures T = 1.5 and 4.2 K. The width of the QWs is selected from the formation condition of the inverted band structure. Shubnikov–de Haas oscillations are measured at two orientations of the magnetic field (perpendicular and parallel) relative to the structure plane. It is established that conduction in the structure under study is occurs via both three-dimensional (3D) substrate electrons and two-dimensional 2D QW electrons under quantum limit conditions for bulk electrons (B > 5 T). The electron concentrations in the substrate and InAs QW are determined. The g-factor for 3D carriers is determined by spin splitting of the zero Landau level. It is shown that the conductance maxima in a magnetic field perpendicular to the structure plane and parallel to the current across the structure in fields B > 9 T correspond to the resonant tunneling of 3D electrons from the emitter substrate into the InAs QW through the 2D electron states of the Landau levels.

Semiconductor nanostructures on the basis of ZnS_xSe_1–x (x = 0, 0.1, 0.3, 0.5, 0.7, and 1.0) compounds are synthesized by the template method based on the formation of semiconductor nanoparticles in porous anodic aluminum-oxide templates upon the vacuum thermal evaporation of a mixture of ZnS and ZnSe powders. The results of studies of the elemental composition of the nanostructures in relation to the composition of the initial mixture and to the parameters of the matrix substrate by means of X-ray photoelectron spectroscopy are reported. It is shown that the composition of the nanostructures is close to the composition of the initial powders and can be specified by the ZnS/ZnSe ratio in the initial mixture.

The influence of the effective concentration of an impurity specifying the conduction type of the base region and the base thickness on the radiation resistance of transistor temperature sensors is investigated. The dependences of the forward voltage drop at the emitter transistor junction and current amplification factor on the magnitude of electron, neutron, and γ-quanta flows are revealed. It is found that degradation of the forward voltage drop under the effect of ionizing radiation begins at doses higher by almost two orders of magnitude than the current amplification factor depending on the transistor’s design features. The reproducibility of the temperature-sensitive parameter, which increases the yield percentage of suitable devices, increases after annealing of the electron-irradiated structures.

The growth of Ge nanocrystals in SiO₂ films is studied in relation to the dose of implanted Ge⁺ ions and the annealing temperature at a pressure of 12 kbar. It is established that the dependences of the nanocrystal dimensions on the content of Ge atoms and the annealing time are described by the corresponding root functions. The nanocrystal radius squared is an exponential function of the inverse temperature. The dependences correspond to the model of the diffusion-controlled mechanism of nanocrystal growth. From the temperature dependence of the nanocrystal dimensions, the diffusion coefficient of Ge in SiO₂ at a pressure of 12 kbar is determined: D = 1.1 × 10^–10 exp(–1.43/kT). An increase in the diffusion coefficient of Ge under pressure is attributed to the change in the activation volume of the formation and migration of point defects. Evidence in favor of the interstitial mechanism of the diffusion of Ge atoms to nanocrystal nuclei in SiO₂ is reported.

The results obtained in the growth of isoparametric InAlGaPAs/GaAs heterostructures are discussed. The composition, structural quality, and luminescence properties of the heterostructures are studied.