Studies of electrical characteristics, deep traps spectra, microcathodoluminescence (MCL) spectra of undoped and donor (Pb, Ca) doped TlBr crystals as influenced by growth conditions (Br pressure, Ar pressure, growth in air) are presented. It is shown that, for the 85−320 K temperature range, the crystal conductivity was determined not by ionic conductance but by the density of electrons and holes supplied by the ionization of deep centers. Centers with activation energies of 1−1.2 eV that pin the Fermi level in donor doped crystals are shown to play a prominent role in the recombination of nonequilibrium charge carriers. In undoped crystals the Fermi level is pinned near Ev+0.8 eV and these centers are also active in the recombination of charge carriers and are responsible for the MCL band peak near 1.85 eV. The temperature dependence of photocurrent in undoped crystals is strongly influenced by electron trapping on relatively shallow centers located 0.1−0.2 eV below the conduction band edge. Deep traps spectra revealed the presence of centers with activation energies 0.36, 0.45, 0.6 eV whose concentration increases with donor doping. Doping with Pb or Ca increases the dark resistivity of the crystals by about an order of magnitude, but Pb doping enhances the density of deep traps, which is not favorable for use of this material in radiation detectors.

A technique for crucibleless growth of single−crystal silicon and its alloys with germanium is developed. For this purpose, the setup of floating zone method was used, which was equipped with additional so−called AHP heater. The heater forms around itself a melt zone that is suspended between the growing crystal, the feeding rod and correspondingly the bottom and the top surfaces of the AHP heater by forces of surface tension. To protect the graphite casing of the heater against the aggressive action of molten silicon, the casing surface was coated with SiC having a special nano−crystalline structure. The system of automation control of the AHP crystallization mode is described. It allows controlling the thermal field near the growing crystal with an accuracy of about 0.05−0.1 K. Numerical computations of heat and mass transfer during the solidification of SixGe1−x alloy with a 2% Si content, as well as shaping of the free Si−Ge melt surface during the crystal pulling were performed. Uniform bulk crystals were obtained. The range of the highest melt layer at which the shaping process remains stable was found to be 10−20 mm. The grown As−doped Si single crystals showed to have strong twining directly caused by presence of the SiC inclusions revealed in the crystal bulk. The possibility to achieve a convex and nearly flat shape of the interface by means of the AHP heater was proved. The layered mechanism of Si crystallization was found to be present during crystal growth on a seed in the [111] direction, with the faceted area under certain conditions occupying almost the entire crystal cross section.

We studied regularities of polymorphous transitions in high−purity powder preparations of metal complex of 8−hydroxyquinoline with aluminum, gallium and indium (Meq3, where Me= Al, Ga, In) in the 300−712 K temperature range. According to the results of luminescent and Raman spectra measurements combined with XRD analysis, the general pattern of the polymorphous transitions in all the investigated compounds is β → α→ δ→ γ → ε. Hybrid materials (HM) were synthesized based on borate glass matrix with 0.02–0.1 wt % Meq3. Bulk samples were obtained by melting, and HM thin films were produced by high vacuum deposition. The luminescent properties of the hybrid materials were studied at room temperature. For the bulk HM an increase in the synthesis duration resulted in the shift of the maximum luminescence peak towards short wavelengths relative to that of pure δ(γ)−Meq3 by 40 nm for Alq3, 15 nm for Gaq3, and 10 nm for Inq3.

Results of application of a ferroelectric LiTaO3 crystal in opto− and acou toelectronics are presented. The large values of the piezoelectric constants in the LiTaO3 crystal are favorable for designing bulk acoustic wave resonators. The possibility of direct electron beam repolarization of LiTaO3 crystals was used for the fabrication of ferroelectric domain structures sizing from few nanometers to tenth micrometers. The regular domain structures in the LiTaO3 crystal were used as an optical diffraction grating and for the generation of second−harmonic optical radiation.

The method of bidomain structure synthesis in lithium niobate single crystal wafers based on the formation of a specific temperature gradient across the sample thickness has been developed. The lithium niobate wafer placed between two silicon wafers was heated due to the absorption of light annealing system radiation by silicon. The work cell design allows one to form and control the power of thermal fluxes entering the ferroelectric wafer thus creating temperature gradients required for a controlled process of formation of two domains with opposite polarization vectors («head to head» domain structure). The efficiency of light absorption for the formation of external thermal sources that allow one to implement symmetric and asymmetric heating, determining the position of the conditional surface with the zero temperature gradient and consequently the position of the domain boundary is experimentally confirmed.In a lithium niobate wafer 1.6 mm in thickness and 60 mm in length, a symmetrical bidomain structure with opposite polarization vectors was formed. The bending strain of cantilevered samples vs applied voltage was investigated in the -300 to +300 V voltage range, the strain amplitude being more than 35 µm. The measurements showed a high linearity and repeatability of the bias voltage vs bending strain curve.

The article reports a theoretical quantum chemical study of the adsorption mechanisms in atomic and molecular hydrogen on the surface of an advanced polymeric material – pyrolized polyacrylonitrile (PPAN). Three variants of atomic hydrogen orientation and five variants of molecular hydrogen orientation over one− and two−layer PPAN surface have been considered. The variants differed in the positions of nitrogen atoms in the close vicinity of a selected adsorption center in the polymer. Potential adsorption energy profiles of atomic hydrogen and hydrogen molecules have been constructed and analyzed, and the main power and geometrical characteristics of the processes have been defined. Charge redistributions in the systems have been studied. We show that neither a hydrogen atom, nor a hydrogen molecule can be adsorbed over the hexagon center of single−layer PPAN surfaces, and in other cases chemical adsorption occurs. For adsorption over the surface of two−layer PPAN, any orientation variants of a hydrogen molecule are possible. A negative influence of nitrogen atom of the polymer surface on the efficiency of atomic hydrogen adsorption has been established, whereas its influence on the adsorption of molecular hydrogen is positive.

We have for the first time determined using the MNDO semiempirical quantum chemical model for a carbon material (CM) structure based on heat treated polyacrylonitrile (PAN) that an increase in the N content from 14 to 18 atoms in CM monoatomic layers C46N14H10, C44N16H12, and C42N18H14 and in the H content from 12 to 22 atoms in CM monoatomic layers C44N16H12 and C44N16H22 leads to a decrease in the binding energy (EB) from 7,40 and 7,12 to 6,88 and 6,25 eV, respectively, and to an increase in the difference between the maximum and minimum bond length (∆l), between the maximum and minimum valence angle (∆θ), and between the maximum and minimum local charge (∆q) from 0,176 Е, 12,0°, and 0,487 to 0,238 Е, 20,8°, and 0,613, respectively, and promotes curving of the CM structure. Quantum chemical simulation results are confirmed by the element analysis of the CM specimens and FeNi3/C nanocomposite. When the IR heating temperature was increased from 30 to 500 °С, the concentrations of N (СN) and H (СH) in the CM and in the FeNi3/C nano-composite decreased from 27 to 18 and 10 wt. % and from 6 to 1 and 0.5 wt. %, respectively.

The effect of thermal annealing of GaN:Mg layers on acceptor impurity activation has been investigated. Hole concentration increased and mobility decreased with an increase in thermal annealing temperature. The sample annealed at 1000 oC demonstrated the lowest value of resistivity. Rapid thermal annealing (annealing with high heating speed) considerably improved the efficiency of Mg activation in the GaN layers. The optimum time of annealing at 1000 oC has been determined. The hole concentration increased by up to 4 times compared to specimens after conventional annealing.

This paper presents results on the simulation of photo converters in a spectral splitting system where solar radiation is separated into three spectral ranges (∆λ1<500 nm, ∆λ2 = 500−725 nm and ∆λ3>725 nm) by means of dichroic filters and then converted to electrical energy by photoconverters based on InGaN/GaN, GaAs/AlGaAs single−junction heterostructures and monocrystalline silicon c−Si. Special attention is paid to the absorption spectrum spreading due to more efficient conversion of the ultraviolet part of the spectrum. The total efficiency of the system varies from 21% to 37% depending on the design of heterostructures.

Possible process options for thinning semiconductor substrates have been analyzed. Experiments have been conducted to assess the efficiency of plasma−chemical etching of (100) orientation single crystal germanium substrates used for growing heteroepitaxial structures of multi−cascade solar cells based on A3B5 semiconductor compounds. The specimens were etched on a reactive ion etching instrument with an induction type high−density plasma source in (SF6 : Ar = 2 : 1) gas mixture through various photoresist masks. For FP−383 photoresist masks with 2, 4 and 6.5 µm windows, the etched layer was 20 µm in depth. For a FN−11 photoresist mask with a 95 µm window, etching reached a depth of 58 µm. The FP−383 masks exhibited thinning from 1.5 to 0.87 µm, and the FN−11 mask thinned from 10 to 8 µm. We show that the etching rate which was 2.1−3.3 µm/min decreases with an increase in mask window width following a power law. We have concluded that plasma−chemical etching is a promising tool for improving the energy and mass parameters of multi−cascade solar cells with conventional and metamorphic structures at the final stage of their fabrication.

The effect of magnetic field treatment on the structure and chemical composition of reduced iron powders has been studied. The methods of transmission electron microscopy, X−ray diffraction and X−ray photoelectron spectroscopy have been used, and corrosion rate has been measured. We show that the processing of powders in an installation having an alternating magnetic field of 0.1 T and a frequency of 21 Hz does not result in any changes to the structure and phase composition. Reduced iron powder particles are spherical; the average diameter is of 2−3 microns, the particles being covered with an amorphous shell. Surface chemical composition studies have shown the shell to be a layer of natural ferric oxide/hydroxide forming in air. A method has been developed for determining the thickness of the oxide shell covering the spherical particles based on the relation of photoelectron lines intensities of the zero−valent and oxidized iron. We show that the shell thickness in magnetic field treated specimens is by 10−20% less than that in untreated powder. Corrosion rate measurements in a corrosive environment have shown that magnetic treatment significantly reduces the oxidation rate of the powders: the more the processing time, the lower the corrosion rate.

Ti/Al/Ni/Au metallization widely used in the technology of GaN base devices have a very important imperfection: rough surface. There are different opinions about the causes of this imperfection: balling−up of molten aluminum or the appearance intermetallic melt phases in the Au–Al system. To check the effect of the former cause, we have studied the formation of rough surface after annealing of Ti/Al metallization which is used as a basis of many metallization systems for GaN. The substrates were made from silicon wafers covered with Si3N4 films (0.15 microns). On these substrates we deposited the Ti(12 nm)/Al(135 nm) metallization system. After this deposition the substrates were annealed in nitrogen for 30 s at 850 оС. The as−annealed specimens were tested for metallization sheet resistivity, appearance and surface morphology.We have shown that during annealing of the Ti/Al metallization system, mutual diffusion of metals and active interaction with the formation of intermetallic phases occur. This makes the metallization system more resistant to following anneals, oxidation and chemical etching. After annealing the surface of the Ti/Al metallization system becomes gently matted. However, large hemispherical convex areas (as in the Ti/Al/Ni/Au metallization system) do not form. Thus, the hypothesis on the balling−up of molten aluminum on the surface of the Ti/Al metallization system has not been confirmed.

We have studied the transformation of radiation defects generated by proton implantation in n−type silicon crystals with a resistivity of 100 Ohm · cm. The measurements were conducted using high−definition X−ray diffraction (HDD). We show that sequential implantation of protons with energies of 100 + 200 + 300 keV and a fluence of 2 · 1016sm−2 results in the formation of a damaged layer with an increased lattice parameter and a thickness of 2.4 mm. This layer is formed by radiation−induced defects both of vacancy and interstitial types. Vacuum annealing of the irradiated crystals at 600 °C enlarges the radiation−induced defects while reducing their number. After annealing at 1100 °C interstitial type defects prevail.