Том 50, № 1 (2016)

The luminescence properties of light-emitting diodes based on GaAs/InGaAs heterostructures containing Mn-doped layers are studied. The dependences of the degree of electroluminescence circular polarization on the growth parameters, specifically, the Mn content and the hole concentration are obtained. A steady increase in the degree of electroluminescence circular polarization and in the Curie temperature of the ferromagnetic structure with increasing hole concentration is observed, and a change in sign of the degree of circular polarization under variations in the Mn content is revealed. The data are interpreted on the basis of well-known models of ferromagnetism in structures based on ferromagnetic semiconductors.

A technology for the production of fully hybrid microcavities on the basis of Zn(S)Se films and amorphous insulating SiO₂/Ta₂O₅ coatings is proposed. The influence of all stages of the manufacturing cycle on the structure of exciton states in the Zn(S)Se films is demonstrated. This influence is reduced to four main effects: the appearance of a fine structure of emission lines related to free excitons; a decrease in the relative contribution of excitons bound at neutral acceptors to the exciton-emission spectrum; a shift of the emission lines related to exciton–impurity complexes and free excitons to lower frequencies; and a decrease in the splitting between emission lines related to heavy and light excitons. Samples of fully hybrid microcavities, in which the high structural and optical quality of Zn(S)Se films is retained, are fabricated.

The correlation parameters of self-organizing structures are investigated using a combined approach, a combination of 2D detrended fluctuation analysis and the average-mutual-information method. The self-organizing structures to be investigated are model surfaces with different degrees of ordering (ordered, disordered, and mixed) and amorphous hydrogenated silicon and tetrahedral carbon films. It is demonstrated using test structures that the correlation vectors determined by kinks on the scale dependence of the fluctuation function with the use of the 2D detrended fluctuation analysis coincide with sufficient accuracy with specified periods of surface harmonic components. It is more expedient to study disordered structures using the average-mutual-information method. The physical meaning of maximum mutual information is shown to characterize the information capacity of a system. The combined approach allows the correlation parameters of combined systems to be investigated most comprehensively.

The spectral complex of optical functions of the calomel Hg₂Cl₂ single crystal is determined in the range 0–20 eV at 300 K in unpolarized light. The spectra of the imaginary part of the permittivity ε₂(E), the bulk–Imε^–1 and the surface–Im(1 + ε)^–1 electron energy losses are decomposed into elementary bands. Their main parameters, including energies and oscillator strengths of the transition bands are determined. Calculations are performed on the basis of the experimental reflectance spectrum of the crystal cleavage. Computer programs based on Kramers–Kronig relations, analytical formulas, and the advanced parameterfree method of combined Argand diagrams are used. The main features of the spectral set of optical functions and the parameters of expansion band components ε₂(E),–Imε^–1, and–Im(1 + ε)^–1 are determined.

The technological conditions for growing single crystals of Tl_1–xIn_1–xSn_xSe₂ (x = 0.1–0.25) alloys are developed. The spectral distribution of the photoconductivity of the grown crystals at T = 300 K and thermally stimulated conductivity are studied. The effect of In³⁺cation substitution with Sn⁴⁺ in Tl_1–xIn_1–xSn_xSe₂ (x = 0.1–0.25) alloys on their photoelectric properties is shown.

Textured nanocrystalline ZnO thin films are synthesized by ion beam assisted deposition. According to X-ray diffraction data, the crystallite size is ~25 nm. Thin (~15 nm) ZnO layers containing Ag nanoparticles are formed in a thin surface region of the films by the implantation of Ag ions with an energy of 30 keV and a dose in the range (0.25–1) × 10¹⁷ ion/cm². The structure and optical properties of the layers are studied. Histograms of the size distribution of Ag nanoparticles are obtained. The average size of the Ag nanoparticles varies from 0.5 to 1.5–2 nm depending on the Ag-ion implantation dose. The optical transmittance of the samples in the visible and ultraviolet regions increases, as the implantation dose is increased. The spectra of the absorption coefficient of the implanted films are calculated in the context of the (absorbing film)/(transparent substrate) model. It is found that the main changes in the optical-density spectra occur in the region of ~380 nm, in which the major contribution to absorption is made by Ag nanoparticles smaller than 0.75 nm in diameter. In this spectral region, absorption gradually decreases, as the Ag-ion irradiation dose is increased. This is attributed to an increase in the average size of the Ag nanoparticles. It is established that the broad surface-plasmon-resonance absorption bands typical of nanocomposite ZnO films with Ag nanoparticles synthesized by ion implantation are defined by the fact that the size of the nanoparticles formed does not exceed 1.5–2 nm.

The complex dielectric function of PbS thin films is studied by spectroscopic ellipsometry in the spectral range from 0.74 to 6.45 eV at a temperature of 293 K. The critical energies are determined to be E₁ = 3.53 eV and E₂ = 4.57 eV. For both energy regions, the best fit is attained at the critical point 2D (m = 0). In addition, the Raman spectra and the optical-absorption spectra of PbS thin films are studied. From the dependence of the quantity (αhν)² on the photon energy hν, the band gap is established at E_g = 0.37 eV.

The possibility of growing the (GaAs)_1–x–y(Ge₂)_x(ZnSe)_y alloy on GaAs substrates by the method of liquid-phase epitaxy from a tin solution–melt is shown. X-ray diffraction shows that the grown film is single-crystal with the (100) orientation and has the sphalerite structure. The crystal-lattice parameter of the film is a_f = 0.56697 nm. The features of the spectral dependence of the photosensitivity are caused by the formation of various complexes of charged components. It is established that the I–V characteristic of such structures is described by the exponential dependence I = I₀exp(qV/ckT) at low voltages (no higher than 0.4 V) and by the power dependence J ~ V^α, where the exponent α varies with increasing voltage at high voltages (V > 0.5 V). The results are treated within the framework of the theory of the drift mechanism of current transfer taking into account the possibility of the exchange of free carriers within the recombination complex.

Recent advances in the fabrication of vertical heterostructures based on graphene and other dielectric and semiconductor single-layer materials, including hexagonal boron nitride and transition-metal dichalcogenides, are reviewed. Significant progress in this field is discussed together with the great prospects for the development of vertical heterostructures for various applications, which are associated, first of all, with reconsideration of the physical principles of the design and operation of device structures based on graphene combined with other 2D materials.

The effect of an external electric field on the states of a shallow donor near a semiconductor surface is numerically simulated. A disk-shaped metal gate is considered as an electric-field source. The wavefunctions and energies of bound states are determined by the finite-element method. The critical characteristics of electron relocation between the donor and gate are determined for various gate diameters and boundary conditions, taking into account dielectric mismatch. The empirical dependences of these characteristics on the geometrical parameters and semiconductor properties are obtained. A simple trial function is proposed, which can be used to calculate the critical parameters using the Ritz variational method.

The effect of photoluminescence polarization memory in nc-Si–SiO_x light-emitting structures containing Si nanoparticles (nc-Si) in an oxide matrix is for the first time studied. The polarization properties of continuous and porous nanostructures passivated in HF vapors (or solutions) are studied. It is established that the polarization memory effect is manifested only after treatment of the structures in HF. The effect is also accompanied by a shift of the photoluminescence peak to shorter wavelengths and by a substantial increase in the photoluminescence intensity. It is found that, in anisotropic nc-Si–SiO_x samples produced by oblique deposition in vacuum, the degree of linear photoluminescence polarization in the sample plane exhibits a noticeable orientation dependence and correlates with the orientation of SiO_x nanocolumns forming the structure of the porous layer. These effects are attributed to the transformation of symmetrically shaped Si nanoparticles into asymmetric elongated nc-Si particles upon etching in HF. In continuous layers, nc-Si particles are oriented randomly, whereas in porous structures, their preferential orientation coincides with the orientation of oxide nanocolumns.

The effect of phosphorus implantation into a 4H-SiC epitaxial layer immediately before the thermal growth of a gate insulator in an atmosphere of dry oxygen on the reliability of the gate insulator is studied. It is found that, together with passivating surface states, the introduction of phosphorus ions leads to insignificant weakening of the dielectric breakdown field and to a decrease in the height of the energy barrier between silicon carbide and the insulator, which is due to the presence of phosphorus atoms at the 4H-SiC/SiO₂ interface and in the bulk of silicon dioxide.

The effect of ultraviolet (UV) illumination on the electrical and spectral characteristics of Schottky-barrier photodiodes based on ZnS single crystals is studied. It is found that irradiation deteriorates their photosensitivity and changes the current–voltage and capacitance–voltage characteristics and the surface profile of the blocking electrode. It is shown that the main reason for a decrease in the photosensitivity of the diodes is the photoinduced drift of mobile donors in the electric field of the barrier. This drift depends on the crystallographic orientation of the surface being irradiated. Another photoinduced process observed in the diodes is photolysis of the ZnS crystal. This process mainly determines the change in the electrical characteristics of the diodes and in the surface profile of the electrode at an insignificant change in the photosensitivity.

The method of mathematical simulation is used to examine the influence exerted by the characteristics of the epitaxial structure and contact grid of photovoltaic laser-power converters on their ohmic loss. The maximum attainable photoconverter efficiency at a Gaussian distribution of the laser-beam intensity on the surface of a photovoltaic converter and at dark-current densities of p–n junctions typical of structures grown by the metal-organic vapor-phase epitaxy (MOVPE) technique are determined. An approach to finding the optimal parameters of GaAs and In_0.24Ga_0.76As/GaAs photovoltaic converters in relation to the optical power being converted is suggested, and the structural parameters for incident-power values of 5, 20, and 50 W at wavelengths of 809 and 1064 nm are determined. It is found that, at laser-light intensities of up to 5 W, >60% efficiency can be achieved in laser-light conversion at a wavelength of 809 nm and >55% efficiency, at a wavelength of 1064 nm.

The conditions in which carbon layers are synthesized on the surface of silicon carbide (SiC) wafers by thermal decomposition are studied. The effect of temperature and composition of the gas atmosphere on the structural properties of the layers being synthesized is analyzed. The conditions in which continuous graphite films with both single-crystal and polycrystalline structure can be obtained are determined.

The list of author affiliations should read as follows:

Ioffe Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia

Saint Petersburg National Research University of Information Technologies, Mechanics and Optics, St. Petersburg, 197101 Russia

e-mail: Sergei_Davydov@mail.ru