Vol 47, No 8 (2018)

The paper considers the current state and prospects for the development of the production of the main material, polycrystalline silicon (polysilicon), used in micro and power electronics and photovoltaics. The dynamics of the polysilicon market dynamics are analyzed. It is noted that the growth in the output of polysilicon is determined by the growing needs of photovoltaics and the global trend towards renewable power generation. It is expected that polysilicon production will grow at a rate faster than 10–15% per annum. For the intensive development of photovoltaics, an important role is played by the development level of polysilicon technology and the availability of this material for the large-scale production of highly efficient solar cells. The main technology used in the industry based on the Siemens process is forecast to remain dominant in the long term. OOO Kremniitechnoprom is developing a state-of-the-art polysilicon production facility based on the original developments and modernization of the Siemens process, which is planned to be implemented in Russia involving leading specialists and enterprises from Germany (SPSC GmbH, GEC GmbH). The new enterprise ensures the maximum production safety, despite the potential risks inherent in the technology, primarily through the guarantee of the performance of modern hardware and process flow schemes, the reliability of the equipment and design solutions, and an emergency protection system. Toxic waste will be processed into safe substances and the end products will be sold. The enterprise will be optimized by key indicators for competitive production, such as the product price, production volume, specific capital investment, and current unit costs.

We carry out an experimental-theoretical study of the process of the equal-channel angular pressing (ECAP) to obtain a bismuth-telluride-based thermoelectric (TE) material. A brief review of the mathematical modeling of the ECAP process is given, and the effect of the design features and temperature of ECAP regimes on the formation of plastic is studied. The results of calculations of the thermally stressed state of the samples at different stages of the ECAP process are presented. The calculations for the ECAP process are carried out using the Lagrange finite element mesh. During the calculation, the mesh is adjusted to the geometry of the die, becoming rarer or finer depending on the magnitude of the plastic deformation to satisfy the specified calculation accuracy and the convergence of the iterative process. We discuss the results of an experimental study of the structure and properties of the samples obtained with the help of ECAP using various methods (X-ray diffractometry and scanning electron microscopy). The TE characteristics of the obtained materials are measured by the Harman method. Comparative methodological calculations of the ECAP process for a bismuth-telluride-based TE material with a change in the parameters determining the formation of grains are performed (the critical plastic deformation as a function of temperature and the power-law dependence of the rate of this deformation). This allowed us to adjust the design model of the ECAP process using the grain size measurements in the TE material. The results of the calculation of the process of grain formation at different temperatures of plastic molding are presented and compared with the experimental data. The practical result of this research is the improved geometry of the die punch and the validated technological regimes of plastic deformation, which allowed obtaining samples with high TE efficiency values.

A new approach is presented that allows solving optimization problems of nanosized semiconductor heterostructures. We have formulated and solved the problem of determining the optimal doping of a barrier layer consisting of a number of sublayers, which provides a preset concentration of electrons in the conduction channel of semiconductor heterostructures. To solve the problem, effective optimization algorithms based on gradient methods are developed. As an example, an Al_0.25GaN/GaN heterostructure with a total barrier layer thickness of 30 nm is considered. The results obtained in the numerical experiment are consistent with the modern trend towards the transition from a homogeneous doping profile to a planar δ-doping in field-effect transistor manufacturing technologies. The developed technique of mathematical simulation and optimization can be used in field-effect transistor manufacturing technologies. The approaches presented in the work create the conditions for the automated design of such structures.

The aim of this work is to study the effect that the process of iron and carbon doping of a GaN epitaxial layer on sapphire can influence (affects) on the features of growth of epitaxial films and their dislocation structure. The following research methods are used in the study: secondary ion mass spectroscopy (SIMS), selective chemical etching of spherical sections, and single-crystal diffractometry. It is shown that carbon doping of a GaN epitaxial layer during growth can lead to a significant decrease in the dislocation density of the epitaxial layers. It is also demonstrated that, for samples doped with iron, a decrease in the number of short dislocations in the bulk of the structure is characteristic; however, a large number of extended dislocations are generated, encouraging iron diffusion into the working regions of the heterostructures, which is confirmed by the iron depth distribution of the layers, measured by the SIMS method.

This work is an experimental justification of the choice of the temperature and time modes designed for the heat treatment of real magnetrons, the end result of which is the initial decomposition of barium carbonate into barium oxide. We experimentally determine the temperatures of polymorphic transitions in barium carbonate and the temperature of the dissociation of barium carbonate in different atmospheres (air, argon, carbon dioxide, and vacuum) for the physical modeling of the processes occurring in pumped magnetrons. The phase composition of a test barium carbonate specimen is determined at room temperature by X-ray phase analysis (XPA) on a diffractometer before and after heating. The effect of the temperature and time of isothermal exposure on the phase composition is experimentally investigated on a high-temperature diffractometer. Using a derivatograph, we analyze the chemical and physicochemical processes that occur in the samples during heating. The enthalpy of polymorphic transitions and the activation energy of dissociation are evaluated. Quantitative data are presented that characterize the kinetics of phase transitions for various heat treatment modes and demonstrate the temperature ranges of the existence of different phases. It is shown that reducing the heating rate and increasing the time of heating interruptions slow down the transition of BaCO₃ into BaO. It is established that the powder is sintered when heating barium carbonate.

The dynamics of fluorine atoms distribution over the thickness of the grown anodic oxide layers and the effective surface charge on InAs crystals under these layers are investigated. Anodic oxidation is performed in an alkaline electrolyte to which a fluorochemical component in the galvanostatic mode is added at the anode current densities of 0.05 and 0.5 mA cm^–2. The layer’s thickness changes by 32–51 nm by setting a final voltage of 15 to 25 V on the electrodes during the growth. The layer’s thickness and refractive index are measured by an ellipsometric technique and the distribution of the thickness of fluorine atoms is measured by photoelectron spectroscopy combined with ion etching. Simultaneously, MIS structures are fabricated from the grown layers and their capacitance–voltage characteristics are calculated to determine the effective surface charge and density of the surface states at different layer thicknesses. The main results of the investigations are that, with regardless of anodic current, density the grown layers are compacted, the fluorine atoms distribution profile shifts toward InAs, and the positive effective surface charge gradually decreases from 3.6 × 10¹¹ to 2.0 × 10¹¹ cm^–2 at densities of the surface states of (6–7) × 10¹¹ eV^–1 cm^–2 in all cases. It is concluded based on comparison of the obtained data with the theoretical concepts on the charge structure of MIS structures that the built-in charge is gradually removed from the interface with InAs during the anodic oxide layer’s growth, which explains the observed decrease in the effective surface charge when the layer’s thickness increases. This result indicates, that the layer’s growth rate is faster than rate of the built-in layer charge shifting toward InAs.