Vol 45, No 6 (2019)

Two different approaches to epitaxy of 4-μm-thick layers of polar GaN(0001) and semipolar GaN(10\(\bar {1}\)1) on a V-shaped nanostructured Si(100) substrate with nanometer-thick SiC and AlN buffer layers have been experimentally demonstrated. The GaN(0001) layers were synthesized by hydride vapor-phase epitaxy, and GaN(10\(\bar {1}\)1) layers, by metal-organic vapor-phase epitaxy, with the growth completed by hydride vapor-phase epitaxy. It was shown that layers of the polar GaN(0002) have a longitudinal elastic stress of –0.45 GPa and the minimum full width at half-maximum of the X-ray diffraction rocking curve ω_θ ~ 45 arcmin, whereas for the semipolar GaN(10\(\bar {1}\)1), these values are –0.29 GPa and ω_θ ~ 22 arcmin, respectively. A conclusion is drawn that the combined technology of semipolar gallium nitride on a silicon (100) substrate is promising.

It is determined experimentally that the luminescence spectrum of a diamond at room temperature contains one or two Gaussian peaks. This result is associated with the exciton–phonon interaction in diamond, which, along with the zero-phonon line, contains phonon repetitions of the first and second order. This phenomenon is characteristic only of natural diamonds and is absent in synthetic samples. Therefore, it can be used to identify cut diamonds.

The hydrodynamic regimes of interaction between a droplet of the fuel water-in-diesel microemulsion with a heated rigid surface are studied, and regime maps are drawn with the separation of constitutive equations and inertia, viscous, and surface tension forces. The critical values of the Weber and Reynolds numbers are established that correspond to transitions between the interaction regimes (thermal disintegration and rebound of the droplet). From the practical point of view, the results may be used in studying the formation processes of air–fuel mixture in the combustion chambers.

The disordering in cadmium mercury telluride solid solution films grown by molecular beam epitaxy on Si and GaAs substrates has been examined by optical transmission and photoluminescence investigations. The effect of a fundamental decrease in the disordering scale under thermal annealing and possible interplay of the observed phenomena with defects typical of films grown by molecular beam epitaxy are discussed.

Specificities of the generalized synchronization mode in unidirectionally coupled delayed oscillators are studied. Four different cases of the interaction of systems characterized by different numbers of positive Lyapunov exponents are considered. It is established that the threshold for the rise of a synchronous mode strongly depends on the degree of chaoticity of interacting systems and the coupling of systems characterized by a different number of positive Lyapunov exponents gives rise to additional synchronization regions.

The results of a study of carrier transfer and recharging of deep levels in semiconductor structures for ionizing radiation detectors are presented. Resistive-type arsenide–gallium structures with Schottky barriers and uniform distribution of deep chromium acceptors and donor EL2 centers have been studied. Solving the continuity and Poisson equations using the commercial design package, the effect of the volume depletion of detector structures by electrons with an increase in the applied voltage has been observed. It is established that the nonlinearity of the volt-ampere characteristics of structures occurs due to a change in the type of conductivity upon transition from an equilibrium to a nonequilibrium state. In this case, structures with initial (equilibrium) hole-type conductivity have close to linear volt–ampere characteristics.

The frequency dependencies of complex impedance \(\dot {Z}\), dielectric permittivity ε, and dielectric loss tangent tanδ of thin (1400 Å ) films V_{1 –x}Ge_xO₂ (for x = 0 and 0.03) are studied in the frequency range of 10‒10⁶ Hz at 300 K. It is found that, at x = 0, the frequency dependence of tanδ has a maximum at a frequency of 100 kHz, whereas at x = 0.03 an additional maximum in the region of 10 kHz is detected. Also, the Cole–Cole diagram of VO₂:Ge films acquires a feature in the form of an additional semicircle. Owing to the extremely high sensitivity of the dielectric spectroscopy method, the proposed equivalent circuit diagram of the sample allowed detecting the existence of two sets of VO₂ nanocrystallites in the V_0.97Ge_0.03O₂ film, including Ge-doped nanocrystallites and practically nondoped ones.

The depth distribution of the energy release (linear energy transfer) occurring upon bombardment of a tungsten target by deuterium atoms with energies ranging from 100 eV to 10 MeV is calculated. It is demonstrated that, contrary to common belief, the maximum energy release at energies below 100 keV is localized near the surface of the solid. At energies above 100 keV, the shape of the distribution changes, and a Bragg maximum emerges near the particle stopping point. The depth distribution of the energy release in tungsten under conditions typical of the ITER tokamak reactor is determined. This distribution provides an opportunity to estimate the wall heating by incident plasma atoms.

The motion of dislocations during low-temperature deformation of two-component alloys has been studied. The condition is found under which the appearance of a region with negative slope of strain-rate dependence of the yield stress is possible that leads to the onset of dynamic instability and jumpwise straining. An analytic expression for the critical magnetic field capable of suppressing these jumps is obtained.

We have theoretically studied the possibility of using the phenomenon of phase switching of coherent population trapping for creating a switch of light propagation direction in electromagnetically induced gratings in a medium with Λ-atoms. The permissible region of this effect application is determined and the parameters are found which ensure the obtaining of a high-efficiency scheme of the spatial redistribution of probing field intensity on atomic density gratings.

The spectral, temperature, and field dependences of the Faraday effect in the IR spectral range have been studied in single crystals of the CoFe₂O₄ ferrimagnetic spinel. It is established that the magneto-optical quality factor of CoFe₂O₄ spinel varies from –60 to +20°/dB in a wavelength range of 1.5–10 μm and weakly depends on the temperature in a 200–300 K interval. Physical mechanisms are proposed that may be responsible for the Faraday effect.

We have evaluated possibilities of using the method of Rutherford backscattering spectrometry (RBS) for depth profiling of multilayer thin-film structures containing nanodmensional layers of elements with close atomic masses. It is established that RBS measurements can ensure high precision determination of the composition of these multilayer structures, total film thickness, and thicknesses of separate layers. This ability can be used for the input quality control of multilayer structures used in micro- and nanotechnologies.

The process of electron instability development and propagation of a cathode electron beam and anomalous ion beam, followed by outburst of current in the initial stage of arc discharge was observed in rarefied plasma cloud of high-voltage vacuum diode. These events are consistent with the model of anomalous ion acceleration in interelectrode plasma at the spark stage of vacuum arc discharge.

Prototype field-effect transistors based on solid solutions of transition metal dichalcogenides (TMDs) have been manufactured, and their spectral characteristics were studied using the photocurrent spectroscopy technique. Results of theoretical estimation of the total optical absorbance of two-dimensional (2D) TMD-based semiconductors of various thicknesses are presented as dependent on the light wavelength with allowance for the multiray interference. It is established that the interference effect significantly contributes to the resulting shapes of spectral characteristics of these optical sensors with variable thickness of TMD-based photosensitive layers.

A new method of processing background oriented schlieren (BOS) images has been tested on an object representing a hot airflow at a given temperature. It is found that the proposed method can provide incorrect results in the case of millimeter-scale objects, and it is established that the errors are related to the use of standard processing software. A modified method of BOS image processing is proposed, and the corresponding software is described.