Volume 51, Nº 3 (2017)

FeIn₂S₄ and CuIn₅S₈ compounds and (FeIn₂S₄)_x · (CuIn₅S₈)_1–x alloy single crystals are grown by planar crystallization. It is shown that both of the initial FeIn₂S₄ and CuIn₅S₈ compounds and alloys on their basis crystallize with the formation of the cubic spinel structure. It is established that the unit-cell parameter a linearly varies with the composition parameter x. By means of nuclear gamma resonance spectroscopy in the transmission mode of measurements, the local states of iron ions in the alloys are studied. For the single crystals grown in the study, thermal expansion is explored using the dilatometry technique, the thermal-expansion coefficients are determined, and the Debye temperature and rms (root-mean-square) dynamic displacements are calculated.

It is shown that measurement of the electric-breakdown field E_br in a classically high magnetic field (H) at T = 4.2 K makes it possible to determine the value of the degree of compensation K in pure germanium with K < 50% much more precisely than at H = 0. The parameter S = E_br/H is introduced and its dependence S = f(K) is calculated; the obtained curve makes it possible to determine K if H and E_br are known. To decrease the resistance of the samples, it is recommended that measurements be carried out under “impurity” illumination. It is shown that the value of E_br is invariable at low intensities of such excitation.

The electrical characteristics of epitaxial layers of n-4H-SiC (CVD) irradiated with 0.9 and 3.5MeV electrons are studied. It is shown that the donor removal rate becomes nearly four times higher as the energy of impinging electrons increases by a factor of 4, although the formation cross section of primary radiation defects (Frenkel pairs in the carbon sublattice) responsible for conductivity compensation of the material is almost energy independent in this range. It is assumed that the reason for the observed differences is the influence exerted by primary knocked-out atoms. First, cascade processes start to manifest themselves with increasing energy of primary knocked-out atoms. Second, the average distance between genetically related Frenkel pairs grows, and, as a consequence, the fraction of defects that do not recombine under irradiation becomes larger. The recombination radius of Frenkel pairs in the carbon sublattice is estimated and the possible charge state of the recombining components is assessed.

The optical properties of semi-insulating GaAs crystals subjected to multienergy hydrogen-ion implantation and treatment in a high-frequency electromagnetic field are studied in the infrared spectral region. It is established that such combined treatment provides a means for substantially increasing the transmittance of GaAs crystals to values characteristic of crystals of high optical quality. On the basis of analysis of the infrared transmittance and reflectance data, Raman spectroscopy data, and atomic-force microscopy data on the surface morphology of the crystals, a physical model is proposed to interpret the effects experimentally observed in the crystals. The model takes into account the interaction of radiation defects with the initial structural defects in the crystals as well as the effect of compensation of defect centers by hydrogen during high-frequency treatment.

For the anisotropic PbSb₂Te₄ single crystal, the effect of temperature and doping with Cu on the reflectance spectrum R(ν) is studied for reflection from a cleavage plane orthogonal to the trigonal axis C₃. It is found that the spectrum is complex in structure and exhibits a sharp increase in the reflectance in the far-infrared region and two minima in the mid-infrared region. It is shown that the experimentally observed feature of the reflectance spectra can be quantitatively described in the context of the Drude–Lorentz theory, with the dielectric function that takes into account the contributions of hole plasma oscillations and two optical lattice vibrations at different frequencies. The static conductivity estimated from optical data is in good agreement with the results of electrical measurements of the dc conductivity.

The temperature and size dependences of the energy gap in CdSe quantum dots with diameters of 2.4, 4.0, and 5.2 nm embedded in fluorophosphate glasses are investigated. It is shown that the temperature coefficient of the band gap dE_g/dT in the quantum dots differs from the bulk value and depends strictly on the dot size. It is found that, furthermore, the energy of each transition in these quantum dots is characterized by an individual temperature coefficient dE/dT.

We investigate the structure, surface morphology, and optical properties of nanostructured ZnO arrays fabricated by pulsed electrodeposition, Ag nanoparticles precipitated from colloidal solutions, and a ZnO/Ag nanocomposite based on them. The electronic and electrical parameters of the ZnO arrays and ZnO/Ag nanocomposites are analyzed by studying the I–V and C–V characteristics. Optimal modes for fabricating the ZnO/Ag heterostructures with the high stability and sensitivity to ultraviolet radiation as promising materials for use in photodetectors, gas sensors, and photocatalysts are determined.

The problem of the efficiency of the controllable formation of arrays of silicon nanoparticles is studied on the basis of detailed investigations of the electronic structure of multilayer nanoperiodic a-SiO_x/SiO₂, a-SiO_x/Аl₂О₃, and a-SiO_x/ZrO₂ compounds. Using synchrotron radiation and the X-ray absorption near edge structure (XANES) spectroscopy technique, a modification is revealed for the investigated structures under the effect of high-temperature annealing at the highest temperature of 1100°C; this modification is attributed to the formation of silicon nanocrystals in the layers of photoluminescent multilayer structures.

The deposition of In_xGa_1–xAs with an indium content of 0.3–0.5 and an average thickness of 3–27 single layers on a GaAs wafer by metalorganic chemical vapor deposition (MOCVD) at low temperatures results in the appearance of thickness and composition modulations in the layers being formed. Such structures can be considered to be intermediate nanostructures between ideal quantum wells and quantum dots. Depending on the average thickness and composition of the layers, the wavelength of the photoluminescence peak for the hybrid InGaAs quantum well–dots nanostructures varies from 950 to 1100 nm. The optimal average In_xGa_1–xAs thicknesses and compositions at which the emission wavelength is the longest with a high quantum efficiency retained are determined.

The capacitance–voltage and conductance–voltage characteristics of InSb-based MIS structures are measured at different probe signal frequencies with the aim of studying the influence exerted by the technological-synthesis conditions on the capacitive properties of these structures. The influence of positive charge built into the insulator on the sample characteristics is discussed. This influence manifests itself as a sharp capacitance “switch” upon changing the polarity of a low-field (E < 10⁶ V/cm) external signal.

p⁺–n₀–n⁺ 4H-SiC diodes with homogeneous avalanche breakdown at 1860 V are fabricated. The pulse current–voltage characteristics are measured in the avalanche-breakdown mode up to a current density of 4000 A/cm². It is shown that the avalanche-breakdown voltage increases with increasing temperature. The following diode parameters are determined: the avalanche resistance (8.6 × 10^–2 Ω cm²), the electron drift velocity in the n₀ base at electric fields higher than 10⁶ V/cm (7.8 × 10⁶ cm/s), and the relative temperature coefficient of the breakdown voltage (2.1 × 10^–4 K^–1).

Pulsed laser deposition is used to produce AlGaAs and GaP thin films (with a thickness of less than 1 μm) on Si substrates. Methods for reducing the number of structural defects in the films are analyzed, and the effect of strains upon AlGaAs/Si and GaP/Si heterostructures is established by Raman spectroscopy. The application of Al_0.3Ga_0.7As and GaP films as wide-gap windows of silicon photoelectric converters is examined. The spectral characteristics of photocells based on Al_0.3Ga_0.7As/Si and GaP/Si heterostructures are studied. The heterostructures can be used as the first p–n junction of a Si-based multijunction photoelectric converter.

A chemical-etching based method for separating GaN/AlN and AlN epitaxial heterostructures grown on silicon with a silicon-carbide buffer layer and transferring them to substrates of any type is developed. GaN/AlN/SiC and AlN/SiC heterostructures 2.5 μm and 18 μm thick, respectively, are separated and transferred to a glass substrate. It is shown that a silicon-carbide buffer layer on silicon, grown by the substitution method, has a developed subsurface structure which allows easy separation of the film from the substrate and promotes the relaxation of elastic energy caused by a difference in thermal-expansion coefficients of the film and substrate. It is shown that mechanical stresses in the film after its separation from the silicon substrate almost completely relaxed.

SnO₂:Sb thin films are grown by pulsed laser deposition with high-speed particle separation on quartz-glass substrates without post-deposition annealing under different deposition conditions in the range of the energy densities on the target from 3.4 to 6.8 J/cm². Their optical, structural, and electrical properties are studied. It is found that the energy density on the target affects the SnO₂:Sb film conductivity and transmittance. The optimum conditions of film growth by the droplet-free pulsed laser deposition method are determined. A resistivity minimum of 1.2 × 10^–3 Ω cm is observed at an energy density on the target of 4.6 J/cm², a substrate temperature of 300°C, and an oxygen pressure of 20 mTorr in the vacuum chamber during deposition.