Vol 45, No 8-9 (2016)

A survey dealing with the technology of the formation of three-dimensional structures in silicon carbide substrates is presented. As for technology, this problem can be solved by variational ion-stimulated plasma-chemical etching, and most successfully by the source of inductively coupled plasma (ICP). Silicon carbide consists of silicon and carbon that form volatile fluorides in the reaction with fluorine. The etching reaction takes place in the interaction of silicon and carbon with reactive intermediates and fluorine ions. That is why the fluorine-containing gas, sulfur hexafluoride SF₆ in most cases (often with an admixture of oxygen and sometimes argon), is used for the plasma-chemical etching of silicon carbide. The materials that do not react with fluorine are applied for masking during the plasma-chemical etching of silicon carbide. The films of metals such as Cu, Al, and Ni are mainly used and silicon oxide is less used. The formation of through-holes in these substrates followed by the metallization of the holes is a particularly important technological concept related to the plasma-chemical etching of the SiC substrates with the deposited GaN epitaxial layers. Examples of the use of ICP sources for the formation of micro- and nanosize three-dimensional structures in silicon carbide are given. Among them, the formation of the through-holes in the substrates of silicon carbide with epitaxial layers of gallium nitride is discussed.

For the first time, the multicrystalline silicon is grown via directed crystallization using a heater submerged into the melt. The interaction of the heater casing material with molten silicon is studied on a model heater in the form of a graphite plate coated with a special structure SiC protective layer. During the crystallization, the plate has been kept on the melt surface and has almost completely overlaid the melt mirror, which favored a significant decrease in the rate of gas exchange between the melt and the atmosphere in the furnace. Marangoni convection was not observed in the absence of the free surface of the melt and the crystal was grown on the reduced melt convection, especially at the final stages of crystallization, when the thickness of the melt layer was inferior to the cross size of the crucible. The crystal is established to have a strongly pronounced columnar structure. The measured specific resistance varies over the ingot height from 1 to 1.3 Ω cm, and the lifetime of minority carriers is about 3.7 μs. The carbon and oxygen content in the ingot has been measured via FTIR spectroscopy, and the carbon concentration through the ingot height is shown to strongly differ from the linear dependence typical of directed crystallization.

This work presents a series of experimental studies to confirm the main theoretical aspects of ionelectron emission and it searches for the possibility of the practical implementation of the operative control method of reactive ion-beam etching processes of different dielectric thin film materials of electronic engineering. The series of experiments was carried out to study the electron emission on the specially formed thinfilm multilayer heterocompositions of Si₃N₄/Si, Ta₂O₅/Al/Si, and Al/TiO₂/Si. The evaluation of the effect of the induced surface potential in the dielectric film on the integral signal of the secondary electrons at reactive ion-beam etching was carried out. The dependence of the emission properties of thin dielectric films on the electric field generated in the dielectric by the surface potential induced by ion beam during reactive ionbeam etching was established. It is noted that the current level of secondary electrons from the surface of dielectric films deposited on the substrates of different materials differ in magnitude; i.e., it is determined by the substrate emission properties. It is shown that the electric field strength arising in the dielectric film under the influence of the induced potential creates the conditions for the emergence of Malter’s emission determined by the properties of its own dielectric and substrate.

Magnetic and electric hyperfine interactions in the near-surface layers of epitaxial films of yttrium-iron garnet of the (111) orientation grown by the liquid-phase epitaxy method are studied by the method of the conversion electron Mössbauer spectroscopy (CEMS). The studies reveal a stoichiometric violation of the anion sublattice in the near-surface layers (≈8 × 10^–8 m) of yttrium iron garnet film and, as a consequence, the formation of two types of d-sites, which is associated with a significant concentration of point defects in the anion sublattice of the near-surface area and the growing weight of the covalent bonding in the transition film–air layer. This also causes the presence of a fixed doublet component corresponding to iron ions in a paramagnetic state with an intermediate degree of valency between +2 and +3. It is shown that interpretation of the spectroscopic results using the Hamiltonian of mixed magnetic and quadrupole interactions makes it possible to obtain a vector diagram of the spatial orientations of the effective magnetic fields at the Fe⁵⁷ nuclei and, as a consequence, to reconstruct the formation mechanism of the resulting vector of the magnetic moment of the yttrium iron garnet epitaxial film. Our studies reveal a slight noncollinearity of ≈4° in the orientations of the magnetic moments in the a- and d-sites of iron. The obtained results complement the picture of the magnetic and electronic hyperfine interactions in the epitaxial ferrite-garnet films and should be considered in the practical applications of the magnetic properties of such materials.

Studying the electronic and structural properties of AlN thin films is an important problem because such films are widely used as a buffer layer when growing GaN-based semiconductor heterostructures on Si substrates. In this paper, we carry out a theoretical investigation of the properties of an Al-terminated AlN(0001) surface in the framework of the density functional theory. Ab initio calculations allow us to analyze the effect of the in-plane lattice strain on the energy of this surface. It is shown that compressive strain causes a decrease in the AlN(0001) surface energy, while tensile strain leads to its increase. Knowing the surface energy values allows us to evaluate the stress of the surface under investigation. In addition, the curvature of the AlN surface is calculated for various AlN film thicknesses in the case of free growth. The obtained values of the surface curvature are in close agreement with the known experimental results.

The features of the manufacturing process, as well as the results of studies on the morphology, electrophysical, and photoelectric properties of photosensitive structures based on silicon containing siliconcarbide and porous silicon layers, are considered. A porous layer is created on the surface of a monocrystalline silicon substrate via electrolytic etching in fluorine-containing solutions. Wafers with a different surface microrelief such as a ground, polished, and textured one, has been used. The carbonization of the samples resulting in the formation of SiC/Si heterostructures has been carried out via gas transport endotaxy in a hydrogen flow using a vertical reactor with cold walls and a graphite container. The structure and composition of the manufactured SiC/Si heterostructures formed on different types of structured surfaces on polycrystalline and monocrystalline silicon, including the surface porous silicon layer, are investigated. It is shown that the process of endotaxy on all the types of surfaces leads to the formation of a single-crystal phase of silicon carbide by cubic modification. Using scanning and transmission electron microscopy, the morphology of the produced structures is investigated. Filiform entities with a different structure have been revealed on nonporous surfaces identified as silicon carbide, whereas the cylindrical or conical structures, whose nature is uncertain, have been observed on porous surfaces. The current-voltage and current-power curves are plotted for all types of manufactured structures, the general form of which indicates the presence of several potential barriers there. The photoelectric properties of the structures and the prospects of their use in photoelectric converters of solar cells are analyzed.

We have studied the influence of the yttrium oxide (Y₂O₃) dopant (1 and 2 mol %) on the phase composition, structure, and electrical properties of ZrO₂–9 mol % Sc₂O₃ solid solution. Stabilization of ZrO₂ jointly with 9 mol % Sc₂O₃ and 2 mol % Y₂O₃ is shown to allow the acquisition of high phase stability transparent homogeneous crystals with a cubic structure. Their mechanical grinding is established to cause no change in the phase composition of these crystals, whereas the powders retain the initial fluorine structure. The powders preserved the original structure of the fluorite crystals. All the probed crystals reveal high microhardness and low fracture toughness. Increasing the Y₂O₃ concentration in the crystals led to a reduction of the maximum loads on the indenter, which the sample withstood without cracking. As is shown, the specific conductivity exhibits nonmonotonic behavior depending on the Y₂O₃ concentration in the crystals. Increasing the Y₂O₃ content to 2 mol % in the solid electrolyte reduces the conductivity of the crystals in the entire temperature range that is attributed to a decrease in the carrier mobility due to the increasing ion radius of the stabilizing ion.