Persons

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A two-step MOCVD-hydride method of fabricating GaN layers has been investigated. Some issues of doping the layers by donor and acceptor impurities have been studied. The laws of the influence of technological modes on the growth rate, structure and the functional characteristics of the quantum-sized heterostructures based on GaN with multiple quantum wells have been determined.

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Main active elements in the frequency range from a few to a hundred gigahertz still are field-effect transistors with Schottky barrier based on gallium arsenide, other AB compounds and various heterostructures based on them. For optoelectronics, gallium phosphide and its compounds are of high importance. As a rule, these heterostructures are obtained by vapor phase methods, the use of which requires correct data on volatile components vapor composition. In this work, arsenic and phosphor vapor composition was studied by tensimetric static method. A mathematical model for processing of experimental results was built. Data on superheated arsenic vapor pressure were obtained using quartz gauge membrane in the range of temperature 973-1173 K and pressure 1,3∙10-1,9∙10 Pa. The calculations have found that arsenic and phosphor vapor mainly consist of two- and four-atomic molecules. Using best documented reference data on As, As, P and P enthalpies and entropies, corresponding thermodynamic values have been determined for As: = (178,90 ± 3,77) kJ/mol, = (227,17 ± 5,44) J/(mol·K); and for P: = (229,01 ± 3,55) kJ/mol, = (156,16 ± 0,83) J/(mol·K).

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Multicomponent solid solutions of AB are increasingly used in optoelectronics, photonics, and other fields of science and technology. These are AlGaInN-based emitters, InGaAsP-based receivers, etc. In addition, these materials are widely used as buffer and isomorphic layers in general-purpose nanoheterostructures. The main methods of their production are gas-phase methods, such as chloride-hydride, MOS-hydride epitaxy, MBE. The development of optimal technological modes of multicomponent layers and structures, as a rule, takes a lot of time and is quite expensive. In this paper, the author proposed a method for modeling processes based on the basic physical and chemical laws of the crystallization processes of materials and the properties of AB compounds. The analysis and prediction of the processes of obtaining four-component solid solutions InGa AsP , isoperiodic with GaAs, three-component solid solutions GaAsPand GaAsP were performed. The calculated modes have been experimentally implemented and the materials corresponding to the current level of quality have been obtained.

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A theoretical analysis of the mechanisms of the gallium nitride crystallization in the process of the gas-phase epitaxy has been performed. The process of layers growth under conditions of the constraints in the boundary layer has been in detail considered. The conditions for the process control and the mass transfer forcing have been determined. The influence of the rotation speed of the substrate on the crystallization mechanism has been experimentally studied.

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The distinctive features of diffraction of the multilayer heterostructures based on gallium nitride have been considered. Using the Vector-GaN installation for the x-ray diffraction the influence of the technological conditions of producing the heterostructure layers GaAlN/InGaN/GaN/AlO on the structural perfection has been revealed.

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The results of the study on the structural perfection of the layers of the heterostrucrure GaN/GaInN/AlO and the impact of the defects on the characteristics of the emitter based on them have been presented. To determine the defectiveness of the layers the x-ray diffraction method has been used. A new methods and a device based on photodiode FD-24K have been developed for estimation of the quantum yield.

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The electro-physical properties of silicon limit its application for opto-electronic elements and for microwave technology devices. In this case silicon is replaced by the material with higher band gap. These materials include the nitrides of the III-group elements, in particular, GaN, AlN, InN and solid solutions based on them. As a result, it becomes possible to manufacture devices with the high efficiency, for example, the light diodes and photoreceivers, capable to operate in a very broad radiation spectrum. Besides, the materials based on GaN are successfully used for creation of powerful microwave devices, such as the transistors with high electron mobility (YEMT) operating at high temperatures. Some technological features of formation of the active layers in heterostructures of AlGaN/GaN/InGaN/GaN MOS using the metal organic compounds have been considered. As the initial substances the high-purity ammonia (NH) and organometallic compounds of gallium, aluminum and indium (MOC Ga, MOC A1 and Mosp) in trimethylene form have been used. The temperature dependence of the growth rate has been investigated in a wide temperature range, which has shown the critical role of the absorption processes on the surface of the growth. To simulate the process and to determine the conditions of forming the composition of solid solutions based on GaN the thermodynamic analysis of patterns in the implementation of the process under study has been performed. It has been found that while obtaining solid solutions in the high temperature range the InN content in them exceeds 0.4 mole frac. and while reducing the growth temperature to 600 °C the conditions of In occurrence in the solid solution are significantly improved and the concentration increases up to 0.9 mole.frac. It has been shown that while growing the GaAlN solid solutions in the wide temperature range it is possible to obtain solid solutions with AlN content from 0.1 to 0.9 mole frac. The experimental studies have confirmed the calculations. Therefore, when growing layers of GaIn N quantum wells in the active region of heterostructures for industrial chips of blue LEDs with the indium content x = 0.1 - 0.15 it is necessary to reduce the growth temperature. However, at low temperatures some difficulties with the growth of the epitaxial layers, having high crystalline quality, arise.

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The static method using a zero-manometer enables with high accuracy to perform measurements of the vapor pressure. The data on the temperature dependence of the substance non-saturated vapor (the condensed phase is absent) in the static experiment allow the determination of the vapor composition. In this work a multi-component system, consisting of molecules, containing the i -th quantity of atoms, has been considered. The mathematical regularities during studying molecular composition of multicomponent vapor have been developed. Jointly with the initial equations the system of n linear equations with n unknowns has been obtained. The system of equations is compatible and has only one solution, as a determinant, composed by the coefficients at unknown partial pressure of the components, differs from zero. The tellurium vapor composition has been investigated by the experimental static method. It has been shown that the tellurium vapor mainly consists of the equilibrium of one-, two- and four atom molecules Te =2Te and Te =2T. The processing of the obtained experimental data has enabled to obtain the equations of the temperature dependence of the constants and to reveal the change of the tellurium average number of atoms in a gas phase in a broad interval of pressures and temperatures.

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When designing a functional heterostructure based on GaN, its manufacturing technology should allow to grow GaN and In GaN layers of n -type conductivity and GaN and Al GaN p -type conductivity. Specially unalloyed epitaxial layers GaN and In GaN have n type of conductivity with electron concentration ranging from 1∙10 to 1∙10 cm. In many works it is reliably established that uncontrolled donors are vacancies in the field of nitrogen atoms in the crystal lattice. These donors form small energy levels in the forbidden zone. The Ge and Si atoms in the GaN semiconductor are small donors. To create highly doped layers with a high concentration of electrons up to 1∙10cm, it is necessary to carry out a special doping with donor impurities during their cultivation. Impurities Si, O, C and structural defects, as a rule, form different neutral and electroactive complexes with each other, which, as studies show, easily disintegrate at temperatures T > 600 K. If there are currently no specific technological problems with obtaining n - layers, then obtaining p -GaN layers was the most difficult problem. It is shown that in the process of obtaining the method of MOCVD doped with GaN acceptors (with a large excess of NH), there is a thermodynamic possibility of localization of acceptors (A) due to the formation of a high concentration of neutral complexes ( A -H). It is established that the decrease in the concentration of the acceptor and, accordingly, hydrogen in the layers will reduce the localization of the acceptor in neutral complexes and simplify the technological task of obtaining low-resistance layers of the hole type of conductivity even at low concentrations of the acceptor. However, this will require the development of new technological methods, since such a task is directly related to the reduction in the epitaxy of GaN hydrogen content and «undesirable» impurities, such as Si, O and C. The optimal expenditure of CpMg, at which in the epitaxial layer the maximally possible concentration of Mg (6-8)·10 cm is achieved, is about 20-30 l/min. To achieve maximum values quantum yield annealing of heterostructures must be necessarily conducted in the temperature range (1063-1073 K).

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The mechanism of GaN crystallization from the gas phase has been analyzed from the standpoint of the Gibbs's classical thermodynamics. In the investigation of forming the neutral complexes of the acceptor impurities with oxygen the main statements of the Reiss and Debye-Huchel's theory have been used. Based on the analysis of the inter-molecular interaction the instability regions in the GaN - InN amd GaN - AIN systems have been revealed. For the MOS-hydride technology the dependencies of variation of the crystallizing solid solution compositions on the vapor-gas phase composition have been determined.

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The chloride-hydride epitaxy is the main gas-phase method for producing the layers for the functional Homo- and heterostructures in micro- and optoelectronics. Nowadays, for producing nanoheterostructures a significant progress in MOS-hydride and molecular beam epitaxy has been made. The method of molecular layering is developing. The emergence of new materials requires the long-term development of optimal technological conditions for their production and therefore it is necessary to create the mathematical, physical and other principles of modeling these processes. The chloride-hydride method continues to be improved for producing relatively thick layers of functional heterostructures. The bases of physical-chemical modeling on an example of chloride-hydride epitaxy have been proposed. In accordance with the concepts of classical thermodynamics as a measure of the system stability is the free energy. For the process of the stationary epitaxial growth the crystallization energy, which for the case of two-dimensional embryo formation is expressed by the Gibbs-Thompson equation, will be this measure. A physical-chemical model of changing the technological modes of gas-phase epitaxy of various compounds under appropriate conditions, under which the compounds with the same degree of disordering are obtained, has been considered. The equations, which permit to use the conditions of already well-developed technology of any material to forecast the conditions of other materials epitaxy of the same type group, have been derived. The obtained regularities are being used to optimize the chloride-hydride process of gallium phosphide epitaxy and solid state solutions based on it. The conditions of the gallium nitride epitaxy coincide well with the conditions of real technological developments of other authors.

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The most important parameter of the LED heterostructures is the value of the external quantum efficiency. However, for the structures used in the manufacture of crystals for blue and white LEDs there is one more requirement: the wavelemgth maximum of the emission spectrum and the variation of its magnitude over the entire area of the structure should be 460±5 nm. Primarily, this is due to the fact that the most applied design of white LEDs the crystals covered with a layer of phosphor of a specific composition, excited by blue radiation, are used. The deviation from the above values of the spectral parameters of heterostructures leads to a sharp deterioration of light and color characteristics of LEDs. In present work the problem of optimizing the design and technology of growing the active region of the radiating structure, consisting of a set of quantum-size Yam GaIn N and wider bandgap GaN barriers, with a specific wavelength maximum of the emission spectrum, is being solved. The calculation of critical thickness of pseudomorphic layer for a range of Poisson ratio from 0 to 0.2 for GaAlN and from 0 to 0.4 for GaInN. The radiation wavelength is defined by both, by the width of the forbidden zone bulk GaIn N, that depending on the molar fraction of indium in quantum wells and by the thickness of QW in the quantum-well layers. From the obtained in the work dependences it has been determined that to obtain the desired wavelength at the maximum of the emission spectrum of 460 nm it is necessary to have the GaIn N layers, containing approximately 10.3% of indium and having pits thickness about 2.5 nm. The influence of the different distribution profile of indium in quantum wells in the external quantum yield, the uniformity of distribution of the radiation wavelength values at the spectrum maximum and the uniformity of distribution of the radiation power on the structure area, have been investigated. In the study of the effect of the number of quantum wells on the properties of heterostructures is shown that to achieve the maximum value of the external quantum yield of radiation, the number of QWS should be from 4 to 5. The best uniformity of the radiation wavelength at the maximum of the spectrum for the square structure is achieved when the number of QW from 5 to 7. Thus, in the present work, the optimum number of quantum wells in the active region of the heterostructure is 5.

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