Volume 50, Nº 5 (2016)

Thermal expansion in the temperature range 80–700 K is studied for two (trigonal and hexagonal) structural modifications of CuIn₅Se₈ single crystals grown by planar crystallization of the melt. From the data, the thermal-expansion coefficients are calculated for both modifications. It is established that, in the temperature range under study, the thermal expansion of both modifications is anisotropic. For the trigonal modification, the thermal-expansion coefficient in the direction of the c axis (α_c) is larger than that in the direction of the orthogonal a axis (α_a). For the hexagonal modification of the CuIn₅Se₈ crystal, the thermal-expansion coefficient in the direction of the c axis exhibits anomalous behavior: as the temperature is increased, the coefficient α_c increases, after which it decreases to negative values, reaches a minimum, and then increases further. Such behavior of the coefficient α_c is associated with the phase transformation of the hexagonal modification of the CuIn₅Se₈ compound into the trigonal modification.

The localization of the transitions in the bulk of the Brillouin zone that form the main structures in the spectra of the imaginary part of the permittivity in the range up to ~7 eV for III–V semiconductors (AlSb, GaSb, InSb, and InAs) is determined using electron density functional theory. It is established that intense transitions occur not only in the vicinity of the high-symmetry axes of the Brillouin zone, but also in some specific large volumes of the irreducible part of the Brillouin zone.

The structural and optical properties of a metamorphic GaAsSb bulk layer grown on a GaAs substrate are studied. As the excitation power density (at a wavelength of 0.65 μm) reaches 9 kW cm⁻² at liquid-nitrogen temperature and 230 kW cm⁻² at room temperature, a superluminescence signal is observed at wave-lengths of 0.943 and 0.992 μm, respectively.

The correlation properties of the structure of nc-Si/a-Si:H films with different volume fractions of the crystalline phase are studied using 2D detrended fluctuation analysis. Study of the surface relief of experimental samples showed that with increasing in volume fraction of the crystalline phase in the nc-Si/a-Si:H films, the size and number of nanoclusters on their surface grow. The size of Si nanocrystals in the a-Si:H matrix (6–8 nm) indicates the formation of coarse nanoclusters due to the self-organization of Si nanocrystals in groups under laser radiation. According to 2D detrended fluctuation analysis data, the number of correlation vectors (harmonic components) in the nc-Si/a-Si:H film structure increased with an increase in the nanocrystal fraction in the films.

The results of experimental studies of the phase composition of oxide nanostructures formed by the local anodic oxidation of a titanium thin film are reported. The data of the phase analysis of titanium-oxide nanostructures are obtained by X-ray photoelectron spectroscopy in the ion profiling mode of measurements. It is established that the surface of titanium-oxide nanostructures 4.5 ± 0.2 nm in height possesses a binding energy of core levels characteristic of TiO₂ (458.4 eV). By analyzing the titanium-oxide nanostructures in depth by X-ray photoelectron spectroscopy, the formation of phases with binding energies of core levels characteristic of Ti₂O₃ (456.6 eV) and TiO (454.8 eV) is established. The results can be used in developing the technological processes of the formation of a future electronic-component base for nanoelectronics on the basis of titanium-oxide nanostructures and probe nanotechnologies.

It is demonstrated that metamorphic GaAs/InAlGaAs/InGaAs heterostructures with InAs/InGaAs quantum wells, which emit light in the 1250–1400 nm spectral range, can be fabricated by molecular-beam epitaxy. The structural and optical properties of the heterostructures are studied by X-ray diffraction analysis, transmission electron microscopy, and the photoluminescence method. Comparative analysis of the integrated photoluminescence intensity of the heterostructures and a reference sample confirm the high efficiency of radiative recombination in the heterostructures. It is confirmed by transmission electron microscopy that dislocations do not penetrate into the active region of the metamorphic heterostructures, where the radiative recombination of carriers occurs.

In this study, piezoresistive and posistor effects in polymer-semiconductor and polymer-ferropiezoceramic composites have been investigated. The results show that composites based on crystallizable polymers, such as PVDF, HDPE, and PP dispersed by semiconductors and ferropiezoelectric fillers have piezoresistive and posistor properties, respectively. At low pressure, charge carriers tunneling through the located thin polymer among filler particles into the barrier define the conductivity of the composite. When pressure value is increased from 0 to 1 MPa, the thickness of the interlayer decreases and tunnel conductivity descends exponentially depending on barrier height. The piezoresistor sensitivity of a composite based on PVDF-70 vol % + Si-30 vol % is higher than a composite based on HDPE-70 vol % + Ge-30 vol %. Furthermore, the posistor properties of polymer composites dispersed by ferropiezoceramic are determined as the maximum resistance that varies significantly with temperature. Posistor effect in composites based on polymer + ferropiezoceramic is associated with the height of the barrier layer, which changes according to properties of filler, polymer, and dielectric permittivity of two-phase composites. The highest specific resistance related to HDPE-70 vol % + BaTiO₃-30 vol % composite was observed at ~403 K.

The properties of protective dielectric layers of aluminum oxide Al₂O₃ applied to prefabricated silicon-nanowire transistor biochips by the plasma enhanced atomic layer deposition (PEALD) method before being housed are studied depending on the deposition and annealing modes. Coating the natural silicon oxide with a nanometer Al₂O₃ layer insignificantly decreases the femtomole sensitivity of biosensors, but provides their stability in bioliquids. In deionized water, transistors with annealed aluminum oxide are closed due to the trapping of negative charges of <(1–10) × 10¹¹ cm⁻² at surface states. The application of a positive potential to the substrate (V_sub > 25 V) makes it possible to eliminate the negative charge and to perform multiple measurements in liquid at least for half a year.

The results of studies of the current–voltage characteristics and of the photoelectric and luminescence properties of a monolithic diode 1 × 64 linear array based on p-InAsSbP/n-InAsSb/n⁺-InAs with the n⁺-InAs-substrate side illuminated and sensitive in the region of 4-μm are reported. An analysis is performed of the mechanisms of current flow in the temperature range of 77–353 K and also of the photosensitivity and the speed of response taking into account the spatial distribution of nonequilibrium radiation and the data of capacitance–voltage measurements.

The forward-pulse isothermal current–voltage characteristics of 4H-SiC junction barrier Schottky rectifiers (JBSs) with a nominal blocking voltage of 1700 V are measured in the temperature range from–80 to +90°C (193–363 K) up to current densities j of ~5600 A/cm² at–80°C and 3000 A/cm² at +90°C. In these measurements, the overheating of the structures relative to the ambient temperature, ΔT, did not exceed several degrees. At higher current densities, the effective injection of minority carriers (holes) into the base of the structures is observed, which is accompanied by the appearance of an S-type differential resistance. The pulsed isothermal current–voltage characteristics are also measured at a temperature of 77 K.

Three laser structures with a single strained InGaAs quantum well of different depths and a GaAs or Al_0.1Ga_0.9As waveguide region are grown by metal-organic chemical vapor deposition. Using the experimentally determined values of the threshold current density and internal differential quantum efficiency, the velocity of electron capture into the quantum well is calculated for each of these structures. It is found that the capture velocity into deep quantum wells is significantly lower than into shallow ones.

The features of the radiation-stimulated changes in the I–V and C–V characteristics of the emitter–base junction in KT3117 transistors are considered. It is shown that an increase in the current through the emitter junction is observed at the initial stage of irradiation (at doses of D < 4000 Gy for the “passive” irradiation mode and D < 5200 Gy for the “active” mode), which is caused by the effect of radiation-stimulated ordering of the defect-containing structure of the p–n junction. It is also shown that the X-ray irradiation (D < 14000 Gy), the subsequent relaxation (96 h), and thermal annealing (2 h at 400 K) of the transistor temperature sensors under investigation result in an increase in their radiation resistance.

Nanocrystalline acanthite-structured silver sulfide of the monoclinic structure and a Ag₂S/Ag nanoheterostructure are produced. The high-temperature X-ray diffraction technique is applied to the in situ study of the (acanthite α-Ag₂S)–(argentite β-Ag₂S) phase transformation in nanocrystalline silver sulfide. The crystal structure of argentite is refined, and it is found that the content of vacant sites in the metal sublattice of argentite exceeds 92%. A model of a resistive switch, whose operation is based on the reversible acanthite–argentite transformation in a Ag₂S/Ag heterostructure, is considered.

The results of quantitative evaluation of the heat accumulation effect during the femtosecond laser microstructuring of the surface of silicon are presented for discussion. In the calculations, the numerical–analytical method is used, in which the dynamics of electronic processes and lattice heating are simulated by the numerical method, and the cooling stage is described on the basis of an analytical solution. The effect of multipulse irradiation on the surface temperature is studied: in the electronic subsystem, as the dependence of the absorbance on the excited carrier density and the dependence of the absorbance on the electron-gas temperature; in the lattice subsystem, as the variation in the absorbance from pulse to pulse. It was shown that, in the low-frequency pulse-repetition mode characteristic of the femtosecond microstructuring of silicon, the heat accumulation effect is controlled not by the residual surface temperature by the time of the next pulse arrival, which corresponds to conventional concepts, but by an increase in the maximum temperature from pulse to pulse, from which cooling begins. The accumulation of the residual temperature of the surface can affect the microstructuring process during irradiation near the evaporation threshold or with increasing pulse-repetition rate.