Том 53, № 11 (2019)

The accumulation of structural damage in GaN under irradiation with accelerated F and Ne ions with energies of 1.3 and 3.2 keV/amu is investigated. It is shown that chemical effects during implantation of fluorine ions within the doses under consideration do not noticeably affect the formation of stable structural damage both in the bulk and on the surface of GaN.

The phase and elemental composition and the temperature dependences of the resistivity and Hall coefficient (temperature range 4.2 K ≤ T ≤ 300 K, magnetic fields B ≤ 0.07 T) are studied in Pb_{1 – x– y}Sn_xFe_yTe alloys with varying matrix composition and iron-impurity concentration along single-crystal ingots synthesized by the Bridgman–Stockbarger method. The distributions of tin and iron along ingots are obtained. Anomalous temperature dependences of the Hall coefficient related to the Fermi-level pinning by the resonance level of iron located in the valence band of the alloys are found. The experimental results are analyzed within the model of transformation of the electronic structure, involving iron level movement with respect to the top of the valence band with increasing tin concentration and temperature. The temperature coefficient of the iron level movement with respect to the midgap is determined. Possible diagrams of transformation of the electronic structure with increasing temperature in alloys with the normal spectrum (0.06 ≤ x ≤ 0.35) are proposed.

The optical properties of float-zone (FZ) silicon irradiated with swift heavy ions (SHI) are studied. In the low-temperature photoluminescence spectra, a broad peak in the range 1.3–1.5 μm is evident along with the well-known X, W, W', R, and C lines. In this case, it is found that, as the irradiation dose is increased in the range 3 × 10¹¹–10¹³ cm^–2, the photoluminescence peak falls and narrows and, at the same time, its maximum shifts to longer wavelengths.

During the powerful picosecond optical pumping of a thin (~1 μm) GaAs layer, a stimulated intense (up to 1 GW/cm²) picosecond emission arises. It is found that the characteristic picosecond relaxation time τ_r of the emission and of the carrier density increase with an increase of the diameter of the pump pulse for a fixed density of the pump-pulse energy. Due to the relation between the density and the temperature of carriers in the case of high-intensity emission (in the saturation state of emission amplification), the time τ_r is associated with the characteristic temperature-relaxation time τ_T of photopumped carriers, which was determined previously theoretically taking into account the emission-induced heating of carriers. The corresponding analytical expressions for τ_r as a function of τ_T are consistent with the above experimental results.

The mechanism of singlet-oxygen generation on the surface of photoexcited nanoporous silicon has been theoretically analyzed. It is shown that the mechanism of singlet-oxygen generation is based on nonradiative energy transfer from nanoporous silicon to an oxygen molecule according to the Dexter exchange mechanism. An analytical expression is obtained, and the probability of energy transfer from nanoporous silicon to an oxygen molecule is numerically estimated. It is shown that its numerical value, on the order of ~(10³–10⁴) s^–1, is in good agreement with the experimental data.

(ZnO/SiO₂)₂₅ thin-film multilayers consisting of nanocrystalline ZnO layers and amorphous SiO₂ spacers with a bilayer thickness from 6 to 10 nm are synthesized in a single deposition process. An analysis of the temperature dependences of the electrical resistivity of (ZnO/SiO₂)₂₅ thin films shows that, in the temperature range of 77–300 K, the dominant conductivity mechanism successively changes from hopping conductivity with a variable hopping length in a narrow energy band near the Fermi level at temperatures of 77–250 K to thermally activated impurity conductivity around room temperature. Using the obtained temperature dependences of the electrical resistivity, the effective density of localized states at the Fermi level and the activation energy of impurity levels are estimated. The effect of heat treatment on the structure and electrical properties of the synthesized films is examined. It is established that in (ZnO/SiO₂)₂₅ thin-film systems at temperatures of 580–600°C, the ZnO and SiO₂ layers chemically interact, which is accompanied by destruction of the multilayer structure and formation of the Zn₂SiO₄ compound with a tetragonal structure (sp. gr. I-42d).

We report the results of systematic Raman spectroscopy studies of Al_xGa_{1 –x}N (x ~ 0.75) layers grown using plasma-assisted molecular beam epitaxy at various stoichiometric conditions and growth fluxes. The high-intensity asymmetric low-frequency peak obeying Bose statistics is discovered in Raman spectra of the layers grown by temperature-modulated epitaxy at strongly Ga-enriched conditions. Theoretical model is developed to explain the origin and the high intensity of the observed low-frequency peak, which is attributed to the presence of excessive metallic gallium in AlGaN layers and can be explained by vibrations of gallium clusters with a diameter of ~1 nm. The nature of the low-frequency peak is similar to that of the boson peak in glasses, which occupies the same frequency range in Raman spectra. We demonstrate the capabilities of Raman spectroscopy as an express and non-destructive technique for optimization of growth conditions of AlGaN layers to achieve simultaneously the atomically-smooth droplet-free surface morphology and the high structural quality.

The time-resolved photoluminescence of quantum-confined InGaAs heterostructures grown on GaAs substrates is studied by time-correlated single photon counting. The heterostructures have different dimensionalities: the structures are formed as quantum dots, quantum wells, and structures of transition dimensionality (quantum well-dots). It is found that the room-temperature photoluminescence decay time of the samples substantially depends on their dimensionality and corresponds to 6, 7, and >20 ns for quantum dots, well-dots, and wells, respectively. It is thought that the presence of localization centers for charge carriers can be responsible for the experimentally observed shortening of the photoluminescence time in the heterostructures.

The types of structural elements and chemical bonds forming an amorphous matrix of chalcogenide glassy semiconductors of the As–Ge–Se system and changes occurring in them depending on the chemical composition are determined using a method for studying the Raman and transmission spectra and density measurements. It is shown that a transition from the elastic to isostatic state and then to the stressed-rigid state occurs in the system under study with increasing arsenic and germanium contents. The observed changes in the Raman spectra and the features of the dependences of optical and other parameters on the chemical composition are explained within the chemical-ordering model, taking into account the existence of local states near the allowed band boundaries.

The basic features of the band structure observed in bulk samples are retained in polycrystalline SmS thin films. Specifically, the bottom of the conduction band is formed from s-type states and there exist donor impurity levels in the band gap, at an energy of 0.04–0.065 eV below the bottom of the conduction band.

Attenuated total reflection infrared spectroscopy is used to determine the free charge carrier concentration in arrays of silicon nanowires with characteristic transverse sizes of 50–100 nm and a length of the order of 10 μm formed on lightly doped crystalline p-type silicon by metal-assisted chemical etching and subjected to the additional thermal-diffusion doping of boron at temperatures of 850–1000°C. It is found that the free hole concentration in arrays varies from 5 × 10¹⁸ to 3 × 10¹⁹ cm^–3 depending on the annealing temperature and is maximal at temperatures of 900–950°C. These results can be used to extend the range of potential application of silicon nanowires in photonics, sensorics, and thermoelectric power converters.

A high-voltage light-emitting diode (LED) flip chip based on an AlInGaN heterostructure is developed and fabricated. The LED flip chip consists of 16 elements connected in series, each of which is a convential LED. The chip with a total area of 1.25 × 1.25 mm is intended for a working current of 20 mA and a forward voltage of 48 V. To improve the current-distribution uniformity over the active region of the chip elements and to minimize the losses of the element area occupied by the n-type contact, the n-type contact pads in them are arranged inside the p-type contact region due to the two-level metallization layout with an intermediate insulating layer of dielectric. The arrangement topology of the contact pads is developed using numerical simulation. An increase in the quantum efficiency of the chip is provided by the application of combinations of metals with a high reflectance at the LED emission wavelength, which are used when fabricating n- and p-type contacts as well as current-carrying strips.

The morphology of CdS nanocrystal arrays self-assembled during the evaporation of a behenic-acid organic matrix on a wetted substrate surface is studied by atomic force microscopy. The dependence of the morphology of nanocrystal arrays on the initial matrix surface is studied. The morphology of nanocrystal arrays noticeably changes from small fractal arrays to a porous submonolayer with an increase in the nanocrystal density. The nature of attractive forces between nanocrystals which prevents their reversible adhesion and ensures their comparatively high mobility in the array composition is proposed.

Thin AlN nanofilms are produced by reactive ion-plasma deposition onto GaAs(100) substrates misoriented with respect to the 〈100〉 direction to different degrees. It is shown that growth on substrates misoriented with respect to the 〈100〉 direction to different degrees results in the formation of AlN films with different phase compositions and crystal states. An increase in the degree of misorientation of the GaAs(100) substrate used for growth influences both the structural quality of AlN nanofilms and their electronic structure, surface morphology, and optical properties. Thus, the morphology, surface composition, and optical functional characteristics of AlN/GaAs(100) heterophase systems can be controlled using differently misoriented GaAs(100) substrates.