Novel technical solutions and ideas for increasing the yield of solar and semiconductor grade polycrystalline silicon processes have been analyzed. The predominant polycrystalline silicon technology is currently still the Siemens process including the conversion of technical grade silicon (synthesized by carbon-thermal reduction of quartzites) to trichlorosilane followed by rectification and hydrogen reduction. The cost of product silicon can be cut down by reducing the trichlorosilane synthesis costs through process and equipment improvement. Advantages, drawbacks and production cost reduction methods have been considered with respect to four common trichlorosilane synthesis processes: hydrogen chloride exposure of technical grade silicon (direct chlorination, DC), homogeneous hydration of tetrachlorosilane (conversion), tetrachlorosilane and hydrogen exposure of silicon (hydro chlorination silicon, HC), and catalyzed tetrachlorosilane and dichlorosilane reaction (redistribution of anti-disproportioning reaction). These processes remain in use and are permanently improved. Catalytic processes play an important role on silicon surface, and understanding their mechanisms can help find novel applications and obtain new results. It has been noted that indispensable components of various equipment and process designs are recycling steps and combined processes including active distillation. They provide for the most complete utilization of raw trichlorosilane, increase the process yield and cut down silicon cost

A theoretical model has been developed that allows one to determine free electron density in n-GaAs from the characteristic points on far-infrared reflection spectra. It was shown that, in this case, it is necessary to take into account the plasmon-phonon coupling (otherwise, the electron density is overestimated). The calculated dependence of electron density, Nopt, on the characteristic wave number, ν₊, which is described by a second degree polynomial, has been obtained.
Twenty-five tellurium-doped gallium arsenide samples were used to measure the electron density in two ways: according to traditional four-contact Hall method (Van der Pauw method) and using the optical method we developed (measurements were carried out at room temperature). Based on the experimental results, the dependence was constructed of the electron density values obtained from the Hall data, N_Hall, on the electron density obtained by the optical method, N_opt. It is shown that this dependence is described by linear function. It is established that the data of optical and electrophysical measurements coincide if the electron density is N_eq = 1.07 ⋅ 10¹⁸ cm^-3, for lower values of the Hall density N_Hall < N_opt, and for large values NHall > Nopt. 
A qualitative model is proposed to explain the results. It has been suggested that tellurium atoms bind to vacancies of arsenic into complexes, as a result of which the electron density decreases. On the surface of the crystal, the concentration of arsenic vacancies is lower and, therefore, the condition N_opt > N_Hall should be satisfied. As the doping level increases, more and more tellurium atoms remain electrically active, so electron density in the volume begins to prevail over the surface one. However, with a further increase in the doping level, the ratio N_Hall/N_opt again decreases, tending to unity. This, probably, is due to the fact that the rate of decomposition of the complexes “tellurium atom + arsenic vacancy” decreases with increasing doping level.

Lithium niobate and lithium tantalate are among the most important and most widely used materials in acousto-optics and acoustoelectronics. These materials have high values of piezoelectric constants, which makes it possible to use these materials as actuators; however, their use is limited by the thermal instability of a lithium niobate crystal and the low Curie temperature (T_C) of a lithium tantalate crystal. LiNb_(1-x)Ta_xO₃ crystals have to overcome the aforementioned limitations of individual compounds.

Crystals LiNb_0.5Ta_0.5O₃ were grown by the Czochralski method, of good quality. Comparative studies of the features of high-temperature single domainization of LiNb_0.5Ta_0.5O₃ crystals have been carried out. The main differences in the technological regimes for single-domainization of congruent LiNb_0.5Ta_0.5O₃ crystals from congruent LiNbO₃ crystals are demonstrated. The parameters of high-temperature electrodiffusion processing LiNb_0.5Ta_0.5O₃ crystals are presented, which make it possible to obtain single-domain crystals for further study of their physical properties.

In this paper, we compare the structure and dielectric properties of the samples of barium titanate ceramics that have been sintered at temperatures of 1100, 1150, 1200, 1250 and 1350 °C and dielectric characteristics of the samples of barium titanate (80 vol.%) — barium ferrite (20 vol.%). It is shown that only samples sintered at the temperature of 1250 and 1350 °C have polarization sufficient for the existence of the piezoelectric effect. For the same samples, the pyroelectric coefficient and reversal polarization significantly exceed those for samples sintered at lower temperatures. Analysis of the samples structure confirmed the dependence of the dielectric properties of the barium titanate ceramics on the grain size and, as a consequence, on the sintering temperature. Based on the studies carried out, the optimal temperature (1250 °С) for obtaining composite samples of barium titanate (80 vol.%) — barium ferrite (20 vol.%) was selected. The temperature dependence of the dielectric constant for the composite samples based on barium ferrite — barium titanate with a sintering temperature of 1250 °C is similar to the dependence for the BaTiO₃ ceramic samples sintered at 1350 °C. At room temperatures, the permittivity of the composite samples is also significantly higher than that of the barium titanate ceramic samples obtained at the same sintering temperatures. The addition of barium ferrite to the barium titanate not only increased the permittivity of the composite, but also led to a diffusing of the ferroelectric phase transition and a shift in the temperature of the maximum of the dielectric constant by 10 degrees towards high temperatures.

The method of plane-transverse bending was used to measure the strength of thin single-crystal plates of undoped InSb with a crystallographic orientation of (100). It was found that the strength of the plates (thickness ≤ 800 μm) depends on their processing. Using a full processing cycle (grinding and chemical polishing) allows to increase the strength of InSb plates by 2 times (from 3.0 to 6.4 kg/mm²). It is shown that the dependence of strength on processing for wafers with (100) orientation is similar to this dependence for wafers (111), while the strength of wafers (111) is 2 times higher. The contact profilometry method was used to measure the roughness of thin plates, which also passed successive processing steps. It was found that during a full cycle of processing, the roughness of InSb plates decreases (R_a from 0.6 to 0.04 μm), leading to a general smoothing of the surface roughness. The strength and roughness of the (100) InSb and GaAs wafers are compared. It was found that the strength of GaAs cut wafers is 2 times higher than the strength of InSb cut wafers and slightly increases after a full cycle of their processing. It was shown that the roughness of GaAs and InSb plates after a full cycle of surface treatment is significantly reduced: 10 times for InSb due to overall surface leveling and 3 times for GaAs (R_z from 2.4 to 0.8 μm) due to a decrease in the peak component. Conducting a full cycle of processing InSb plates can increase their strength by removing broken layers by sequential operations and reducing the risk of mechanical damage.

The influence of the coupling effect on the parameters of field Hall elements based on thin-film MOS transistors has been studied. Analysis of the development of today’s microelectronics shows the necessity of developing the element base for high performance sensors based on silicon technologies. One way to significantly improve the performance of sensing elements including magnetic field sensors is the use of thin-film transistors on the basis of silicon on insulator (SOI) structures. It has been shown that field Hall sensors (FHS) may become the basis of high-performance magnetic field sensors employing the coupling effect occurring in the double gate vertical topology of these sensing elements. Electrophysical studies of FHS have been conducted for different gate bias and power supply modes. The results show that the coupling effect between the gates occurs in FHS if the thickness of the working layer between the gates is 200 nm. This effect leads to an increase in the effective carrier mobility and hence an increase in the magnetic sensitivity of the material. Thus field Hall elements based on thin-film transistors fabricated using silicon technologies provide for a substantial increase in the magnetic sensitivity of the elements and allow their application in highly reliable magnetic field sensors.

Review on the paper Wuzong Zhou, Reversed Crystal Growth. Crystals. 2019; 9(1): 7 (16 pp). https://doi.org/10.3390/cryst9010007

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