Vol 52, No 9 (2018)

Numerical calculations of the accumulation kinetics of point defects—vacancies and divacancies—under the irradiation of Si with ions having masses of M₁ ≤ 31 amu and energies of E ≤ 100 keV under various irradiation conditions are performed. The previously proposed diffusion-coagulation model is used without application of the “weak diffusion” approximation, which was performed during its analytical implementation. The main peculiarities of the dependences of the concentrations of vacancies and divacancies on the dose, ion-current density, and temperature under irradiation are analyzed. A physical interpretation of these results is given. The developed computing complex is rather flexible and makes it possible to analyze the influence of model input parameters by means of their variation and include additional processes into consideration if necessary.

The study of high-dose carbon-ion implantation without post-process annealing reveals significant modification of the morphology, surface-layer phase composition, and field-emission properties of silicon wafers. The effect of the electrical conductivity type on the evolution of the silicon-crystal surface morphology, upon a variation in the irradiation dose, and a high content of diamond-like phases in the region of microprotrusions at the maximum dose regardless of the electrical conductivity type are found. It is demonstrated that the high-dose implantation of carbon in silicon wafers with a pre-structured surface increases the maximum density of field-emission currents by more than two orders of magnitude.

It is proposed that the Poole–Frenkel effect be applied to predict radiation-induced charge accumulation in thermal silicon dioxide. Various conduction mechanisms of thermal silicon dioxide are considered, the conditions of the appearance of the Poole–Frenkel effect in it are determined, and the characteristics of donor centers participating in Poole–Frenkel electrical conductivity are calculated. A donor center level at an energy of 2.34 eV below the conduction-band bottom is determined and the concentration of ionized donor centers of 1.0 × 10⁹ cm^–3 at 400 K and a field strength of 10 MV/cm is found. It is concluded that the Poole–Frenkel effect can be applied not for prediction of the absolute value of the radiation-induced charge but for comparison of the samples in terms of the ability to accumulate it.

A nanocomposite in the form of monodisperse spherical mesoporous silica particles (mSiO₂) filled with GaN:Eu³⁺ is synthesized by the template method. The method is based on the capillary impregnation of pores of mSiO₂ particles with a melt of crystal hydrates of gallium and europium (0.22 wt %) nitrates, followed by thermal decomposition and ammonia treatment. It is shown that nanocomposite particles contain hexagonal GaN:Eu³⁺, are of spherical shape, monodisperse and do not coalesce with each other. The photoluminescence spectra of the mSiO₂/GaN:Eu³⁺ particles show a group of lines characteristic of intracenter transitions in Eu³⁺.

The results of studies of the optical properties of ensembles of colloidal CdS quantum dots passivated by thioglycolic acid are reported. The average dimensions of the quantum dots lie in the range from 1.7 to 5.8 nm. By X-ray diffraction studies and Raman spectroscopy, it is established that quantum dots crystallize with the formation of a cubic crystal lattice. The systematic features of the quantum-confinement effect in the optical absorption and luminescence spectra, as well as in the luminescence excitation spectra, are established. The features manifest themselves as a blue shift of the corresponding bands with decreasing quantum-dot dimensions. From analysis of the nanosecond luminescence kinetics, it is concluded that experimentally observed radiative recombination proceeds by the donor–acceptor mechanism.

A method for creation of Ge/Si structures with space-arranged nanoislands by heteroepitaxy on the pre-patterned Si(001) substrates with a square grid of the etched pits is developed. The influence of depth and inter-pit spacing on the nucleation and growth of Ge(Si) nanoislands is studied. It is shown, that the nanoislands are formed either inside pits or at their periphery depending on the pit depth. It is found that the size of the nanoislands grown inside the pits goes up with the increase of the inter-pit distance from 1 to 4 μm. The pronounced photoluminescence signal related with the space-arranged arrays of quantum dots with a period of 1 μm is observed in the range of energies from 0.9 to 1.0 eV.

The dielectric relaxation processes in Ge_28.5Pb₁₅S_56.5 glassy system are investigated. The introduction of an iron impurity into a glass matrix is shown to sharply increase the permittivity ε' and decrease the dissipation factor tanδ. The found regularities are explained within the cluster structure (two-phase) model of doped glass.

The properties of porous GaAs samples produced by the electrochemical etching of single-crystal n-GaAs(100) wafers are studied by X-ray diffraction analysis, electron microscopy, and infrared and ultraviolet spectroscopy. It is possible to show that, by choosing the composition of the electrolyte and the conditions of etching, samples can be produced not only with different degrees of porosity and pore sizes (nanopores/micropores), but with another type of sample surface as well. The etching of n-GaAs(100) wafers under the conditions chosen in the study does not change the orientation of the porous layer with respect to the orientation of the single-crystal GaAs(100) substrate. At the same time, etching induces a decrease in the half-width of the diffraction peak compared to that for the initial wafer, a splitting of the phonon mode in the infrared spectra and a partial shift of the components in accordance with the parameters of anodic etching, and a change in the optical properties in the ultraviolet region.

The study is concerned with light-emitting Ge nanocrystals formed during the annealing of Ge_x[SiO₂]_{1 –x} films produced by the high-vacuum cosputtering of germanium and quartz targets onto substrates at a temperature of 100°C. In accordance with the conditions of growth, the Ge molar fraction was varied from 10 to 40%. By means of electron microscopy and Raman spectroscopy, amorphous Ge nanoclusters ~4–5 nm in dimensions are detected in as-deposited films with a Ge content higher than 20 mol %. To crystallize amorphous nanoclusters, annealing at temperatures of up to 650°C is used. The kinetics of the crystallization of Ge nanoclusters is studied, and it is established that up to ~1/3 of the amorphous phase is retained in the system, supposedly at the interfaces between nanocrystals and the surrounding amorphous SiO₂ matrix. It is found that, upon annealing in normal atmosphere, germanium nanoclusters are partially or completely oxidized (at a Ge molar fraction of 30% and smaller). An intense infrared photoluminescence signal from quantum-confined Ge nanocrystals and a visible photoluminescence signal defined by defect complexes (oxygen vacancy + excess Ge atoms) are observed.

The temperature dependences of the current–voltage characteristics and photosensitivity of composite layers of silicon and gold nanoparticles on single-crystal silicon with p-type conductivity are investigated. The current transfer mechanisms in the structures and their influence on the photosensitivity of structures with different amounts of gold in the composite layer are determined.

It is shown that heating of a fullerite film several monomolecular layers thick deposited onto single-layer graphene formed on a substrate of molybdenum carbide Mo₂C at T = 700–800 K leads to the intercalation of C₆₀ molecules under the graphene layer. The direct deposition of C₆₀ molecules at T = 650 K also leads to the intercalation of C₆₀ molecules under graphene; the maximal amount of fullerene accumulated under graphene is one single layer.

A heterostructure promising for designing a backward diode is formed from a zinc-oxide nanorod array and a nanostructured copper-iodide film. The effect of modes of successive ionic layer adsorption and reaction (SILAR) deposition and the subsequent iodization of CuI films on smooth glass, mica, and fluorine-doped tin oxide (FTO) substrates and on the surface of electrodeposited nanostructured zinc-oxide arrays on the film structure and electrical and optical properties is investigated. A connection between the observed variations in the structure and properties of this material and intrinsic and iodination-induced point defects is established. It is found that the cause and condition for creating a backward-diode heterostructure based on a zinc-oxide nanoarray formed by pulsed electrodeposition and a copper-iodide film grown by the SILAR method is the formation of a p⁺-CuI degenerate semiconductor by the excessive iodination of layers of this nanostructured material through its developed surface. The n-ZnO/p⁺-CuI barrier heterostructure, which is fabricated for the first time, has the I–V characteristic of a backward diode, the curvature factor of which (γ = 12 V^–1) confirms its high Q factor.

The possibility of significant lowering of the interband lasing threshold in laser structures of the mid-infrared region based on HgCdTe with HgTe quantum wells by doping with donors, which introduce δ layers near quantum wells, is proposed and analyzed. It is shown that at an optimum surface donor concentration in the δ layer of 4 × 10¹⁰ cm^–2 and an operating temperature of >40 K, the lasing threshold at a wavelength of 20 μm can be lowered more than twofold.

The Raman spectra of thick (~100 μm and more) GaN layers grown on crystalline SiC substrates by the sublimation sandwich method are studied. Good agreement between the spectra of the SiC substrates used in the study and published data indicates that the measurements made in the study are reliable. The minimum difference between the results of the measurements and published evidence for GaN layers means that the layers grown by the sublimation sandwich method in the study compare well with those fabricated by the metalorganic vapor phase epitaxy (MOVPE) or chloride-hydride vapor phase epitaxy (CHVPE) techniques.