Volume 52, Nº 10 (2018)

Samples of (TlGaSe₂)_1 – x(TlInS₂)_x solid solutions are synthesized. The frequency dependences (2 × 10¹–10⁶ Hz) of components of the total complex impedance are studied by the impedance spectroscopy technique and relaxation processes are investigated depending on the composition of the (TlGaSe₂)_1 – x(TlInS₂)_x solid solution in the solubility region (x = 0–0.4). Corresponding diagrams on the (Z''–Z') complex plane are analyzed using the equivalent substitutional circuit method. An anomaly in the temperature dependence of the electrical conductivity, which manifests itself in an abrupt increase in the conductivity, is found for the studied (TlGaSe₂)_1 – x(TlInS₂)_x solid solution at 400 K. This peculiarity is associated with the phase transition into the superionic state.

The emission spectra of structures based on ZnO films deposited by high-frequency magnetron sputtering are studied. Clearly pronounced emission lines associated with the recombination of free (λ = 363 nm) and bound excitons (λ = 377, 390, 410 nm) are observed in the PL (photoluminescence) spectra (T = 300 K) of n-ZnO/p-GaN:Mg structures, and no substantial emission is observed in the impurity PL region λ = 450–600 nm. Only emission lines characteristic of n-ZnO (λ = 374 nm) are observed in the EL (electroluminescence) spectra of n-ZnO/p-ZnO structures (T = 300 K).

Photovoltaic structures on the basis of GaAs p–i–n junctions with a different number of In_0.4Ga_0.6As layers in the space-charge region forming quantum-confined objects are experimentally and theoretically investigated. For all structures, the dependences of the open-circuit voltage on the solar-irradiation concentration are analyzed. It is shown that the implantation of quantum objects leads to the dominance of recombination in them over recombination in the matrix, which manifests itself in a drop in the open-circuit-voltage. An increase in the number of In_0.4Ga_0.6As layers leads to a proportional increase in the recombination rate, which is expressed in a proportional increase in the “saturation” current and corresponds to the model proposed in the study.

The effect of various operating conditions of time-modulated DC (direct current) plasma on the formation of an amorphous a-SiO_x:H matrix and silicon nanoclusters is studied using IR (infrared) and photoluminescence spectra. DC-plasma modulation consists in repeated (n = 180) switching off and on of the magnetron magnet coil with various time combinations, t_off = 1, 2, 5, 10, 15 s and t_on = 5, 10, 15 s, respectively, at a fixed oxygen concentration (\({{C}_{{{{{\text{O}}}_{{\text{2}}}}}}}\) = 15.5 mol %) in a (SiH₄ + Ar + О₂) gas mixture. The positive effect of self-induction on the formation of both the amorphous matrix and silicon nanoclusters is confirmed. The largest values of x in a-SiO_x:H and photoluminescence intensity are observed in the case of the combination of prolonged plasma residence in the working state (t_on = 10–15 s) and the maximum magnetic-field strength. The effect of t_off on the processes of the formation of both the a-SiO_x:H matrix and silicon nanoclusters is also noted.

The problem of the optimal choice of parameters of the empirical tight-binding method to simulate the quantum-confined levels of Si nanocrystals embedded into an amorphous SiO₂ matrix is studied. To account for tunneling from nanocrystals to SiO₂, the amorphous matrix is considered as a virtual crystal with a band structure similar to that of SiO₂ β-cristobalite and with a lattice constant matched to the lattice constant of bulk Si. The electron density distributions in k space for electrons and holes quantum-confined in a Si nanocrystal in SiO₂ are calculated in a wide energy region, which provides a means to see clearly the possibility of the existence of efficient direct optical transitions for hot electrons at the upper quantum-confined levels.

Studies of an electrostatic system of flat metal–semiconductor contacts with a Schottky barrier reveals a nontrivial dependence of their current and voltage photosensitivity (the photovoltaic effect) on the contact shape. The specific features of using the photovoltaic effect in such contacts are determined, to a great extent, by the built-in periphery electrostatic field with an absolute value that depends on the contact perimeter and area. Thus, to increase the efficiency of light-to-electrical energy conversion by Schottky contacts, it is necessary to use optimization techniques based on the concepts of the proposed physical model of an electrostatic system of flat Schottky contacts with regard to periphery electrostatic fields. The “hot electron resonance” effect, which enhances the external quantum efficiency of photodiodes with a Schottky barrier, can be explained by enhancement of the field emission of electrons by the periphery electrostatic field.

For the first time, hot-carrier degradation (HCD) is simulated in non-planar field-effect transistors with a fin-shaped channel (FinFETs). For this purpose, a physical model considering single-carrier and multiple-carrier silicon–hydrogen bond breaking processes and their superpositions is used. To calculate the bond-dissociation rate, carrier energy distribution functions are used, which are determined by solving the Boltzmann transport equation. A HCD analysis shows that degradation is localized in the channel region adjacent to the transistor drain in the top channel-wall region. Good agreement between the experimental and calculated degradation characteristics is achieved with the same model parameters which were used for HCD reproduction in planar short-channel transistors and high-power semiconductor devices.

The effect of low-dose proton irradiation (irradiation dose 10¹⁰–1.8 × 10¹¹ cm^–2) on the capacitance–voltage, forward current–voltage, and reverse-recovery characteristics of 4H-SiC p–n_o junction diodes is studied. Irradiation is performed with 1.8-MeV protons through a 10-μm-thick Ni-film (the proton energy and Ni-film thickness were chosen so that the projected proton range in silicon carbide is approximately equal to the p–n_o junction depth). It is shown that proton irradiation in the above doses (i) does not change the concentration of majority carriers, (ii) leads to a dramatic decrease in the lifetime of nonequilibrium carriers (at a low injection level) (by several tens of times at the highest irradiation dose), and (iii) decreases the reverse-recovery charge at a high injection level (by up to a factor of 3 at the highest irradiation dose).

A comprehensive study (X-ray phase analysis, Raman spectroscopy, and IR reflectance measurements) of p-Sb₂Te_3 – xSe_x (0 ≤ x ≤ 0.10) crystals synthesized by the Czochralski method is carried out. The X-ray phase data and Raman spectra show that all of the alloy samples under study are rhombohedral crystals in structure, with unit-cell parameters close to those of Sb₂Te₃ crystals. At the same time, the formation of regions with different degrees of the replacement of Te atoms with Se atoms is observed. The reflectance spectra of the crystals, R(ν), have a characteristic minimum at about 1000 cm^–1. The minimum is attributed to hole plasma vibrations. The plasma minimum systematically shifts to higher frequencies, as the Se content is increased. Calculation of the reflectance spectra in the context of the Drude–Lorentz model satisfactorily describes the experimental data; in this case, it is necessary to take into account also the contribution of optical crystal-lattice vibrations to spectra in the low-frequency region. The calculation makes it possible to determine the optical parameters of the crystals and to estimate the hole effective mass and the optical conductivity.

FeIn₂S₂Se₂ single crystals are grown for the first time by the Bridgman method, and their composition and properties are determined. It is found that the single crystals are hexagonal in structure. The arrangement of Fe ions in the structure of the FeIn₂S₂Se₂ crystals is studied by nuclear γ-resonance spectroscopy. From the transmittance spectra in the region of the fundamental absorption edge, the band gap of the single crystals grown in the study is determined.

The systematized results of studies of the composition, morphology, structure, optical properties, and conductivity of hydrochemically deposited copper(I) selenide thin films (Cu_1.8Se) with the thickness of 390–400 nm are reported. The studies are carried out using scanning electron microscopy, energy-dispersive analysis, X-ray diffraction analysis, and X-ray photoelectron spectroscopy. The hole conductivity of the layers is established by the thermopower technique. The optical band gap determined from the results of studies of optical absorbance and diffuse reflection spectra of the films at 298 K is 2.5 and 1.84 eV for direct and indirect optical transitions, respectively.

The optical characteristics and structural features of self-assembling nanostructured indium–tin oxide (ITO) films deposited onto substrates heated above 400°C are studied. Estimations of the distribution profiles of the material and effective refractive index in the films under study are obtained by computer simulation of a medium having spectral dependences of light transmission and reflection coefficients closest to those observed in the experiment. These results are in good agreement with scanning electron microscopy data for these films and make it possible to not only confirm the gradient character of such coatings but also restore some of its features. The further overgrowth of voids in self-assembling nanostructured films by means of the deposition of an additional material amount by magnetron sputtering at room temperature leads to a variation in the effective refractive index profile in them. Thus, it is possible to form transparent conductive films with an efficient refractive index profile adjusted for specific tasks. Adjustment of the refractive index profile in self-assembled ITO films acquires a special value for designing coatings with specified properties by virtue of a limited set of transparent conductive materials.

The formation of nanostructures on the surface of GaAs under quasi-equilibrium conditions in a quasi-closed volume from saturated phosphor and indium vapors in the presence of a Au catalyst with growth according to the “vapor–liquid–crystal” mechanism is considered for the first time. The influence of the growth temperature and size of Au drops on the morphology and composition of the fabricated nanostructures is studied. Experimental data on the formation of Ga(In)AsP nanocrystals on GaAs substrates with various orientations are presented. It is established that the temperature growth range of the nanostructures when using this method is 540–640°C with a drop size from 30 to 120 nm. It is shown that the size of the catalyst drops substantially affects the morphology and growth rate of the fabricated nanostructures while their composition weakly depends on both the drop size and the substrate orientation.