Mikroèlektronika

The model-based study of SF₆ plasma composition in respect to both neutral and charged components in a wide range of electron density was carried out. The key plasma chemical processes determining steady-state densities if fluorine atoms under conditions of low- and high-density plasmas were figured out. It was shown that optimized (reduced by the exclusion of non-effective reactions) kinetic schemes provide the satisfactory agreement between modeling results and experimental data from literature sources.

Semiconductor charge qubits based on a double quantum dot in an optical microcavity (a photonic crystal defect) are considered taking into account deviations of parameters from preset ones. Influence of topological disorder of a photonic crystal structure on microcavity spectrum and effect of a stochastic field of external charges on the qubit state are analyzed. Ways to attenuate these effects and to optimize the qubit state storage are indicated.

A model and methodology for simulation of memristive crossbar arrays have been developed taking into account voltage drops on interconnections, the step of tuning the conductivity levels of memristive elements and the nonlinearity of their IV characteristics. The results of testing a spiking neural network in the inference mode in the problem of image recognition using the developed methodology of simulation taking into account the characteristics of experimentally manufactured memristor structures have been obtained.

Using density functional theory (DFT), the electronic structure, lattice parameters, magnetic and thermodynamic properties of TlIn_1–xCr_xS₂ with a monoclinic system were calculated. The influence of the degree of doping with chromium impurities on the properties of TlIn_1–xCr_xS₂ supercells has been studied. Calculations were carried out using ab initio methods in the local electron density approximation (LDA) and in the generalized gradient approximation (GGA). Spin-orbit and Coulomb interactions were taken into account in DFT calculations. A change in the concentration of chromium impurity (x = 0.001–0.02) in TlInS₂ does not lead to a change in the equilibrium lattice parameters and the type of magnetic ordering in TlIn_1–xCr_xS₂.

Phase equilibria and stability of binary and ternary compounds were studied by the thermodynamic method and the functional DFT GGA method in the Tl–In–S ternary system. The constructed isothermal section of the phase diagram at 298 K confirms the insignificant region of homogeneity, based on intermediate ternary compounds, of the Tl–In–S system. The formation energies of the compounds TlInS₂ and TlIn_1–xCr_xS₂ (x = 0.001–0.02) were calculated by the DFT method and are thermodynamically consistent with each other. The energy of formation of the TlInS₂ compound, calculated by theoretical methods, is also consistent with experimental data.

This indicates the adequacy of the calculation models used. In order to determine stable doping conditions, we analyzed the thermodynamic properties of the phases of the Tl–In–S system, established stable states of multicomponent phases, stable equilibria between binary and ternary compounds of the TlIn_1–xCr_xS₂ system.

Polycrystals were synthesized and TlIn_1–xCr_xS₂ single crystals with different chromium impurity concentrations (x = 0, 0.001 and 0.02) were grown from them. The crystal structure, thermodynamic, dielectric, electrical and dosimetric characteristics of TlIn_1–xCr_xS₂ single crystals were studied. The calculated thermodynamic and physical properties of the TlIn_1–xCr_xS₂ phases are compared with experimental data.

Using molecular beam epitaxy (MBE) with plasma-activated nitrogen, III-nitride HEMT heterostructures with an ultrathin AlN barrier were obtained. The effects of nucleation and buffer layer growth conditions on the crystalline quality, surface morphology, and electrophysical properties of the experimental heterostructures were studied. The sheet resistance of the optimized heterostructure was less than 230 Ω/□. Test microwave transistor samples with Schottky gates were fabricated. A parametric model of the HEMT based on the AlN/GaN heterostructure was proposed.

The comparative study of plasma electro-physical parameters, fluorine atom densities as well as Si and SiO₂ etching kinetics in CF₄ + Ar/He, CHF₃ + Ar/He and C₄F₈ + Ar/He gas mixtures with variable (0–45% He) initial compositions was carried out. It was found that the substitution of Ar by He at constant fraction of fluorocarbon component a) disturbs electrons-related plasma characteristics; b) exhibits the very weal effect in the ion bombardment intensity; and c) causes a decrease in both Si and SiO₂ etching rates together with the fluorine atom density. It was shown that the dominant etching mechanism is the heterogeneous chemical reaction while the effective reaction probability either increases (in CF₄ plasma) or keeps the nearly constant value (in CHF₃ and C₄F₈ plasmas) with increasing fraction of He in a feed gas. The mechanism providing above effects were suggested.