The compositions of epitaxial layers forming quantum-well heterostructures AlxGayIn1-x-yAs / InP for laser diodes with the radiation wavelength of 1.55 μm are calculated. When carrying out the calculations, the problem was to provide the maximum height of the energy barriers for effective limitation of charge carriers in the quantum wells. Along with taking care of the effects of the dimensional quantization of the energy of free charge carriers in allowed zones, the effect of elastic stress in epitaxial layers on the displacement of the edges of the energy bands were taken into account in the calculation. It is shown that in order to solve the posed problems it is necessary to form heterostructures with elastic compression stress in a quantum well and elastic tensile stress in the barrier layers. As a result of the calculations the authors suggest a structure that includes a barrier layer of Al0.28Ga0.30In0.42As with a thickness of 110 Å and a quantum well Al0.03Ga0.23In0.74As in a layer with a thickness of 55Å (with the mismatch between the parameters of the crystal lattice and the InP substrate - 0.8% and + 1.4 %, respectively). According to the calculation results, the indicated thicknesses of epitaxial layers do not exceed the critical values that can lead to the formation of imperfect dislocations at heterointerfaces.

Abstract—The Cu2 – xSe (0.03 ≤ x ≤ 0.23) powders fabricated by mechanochemical synthesis have been studied by X-ray diffraction. The in situ study has been carried out for the temperature dependences of the lattice parameters, the structures, and the phase compositions of the powders in the temperature range 25–350°C. The powder compositions are shown to differ from the charge compositions and are shifted to lower copper concentrations. The estimation of peak half-widths of the cubic β phase indicates an increase in the structure imperfection after the phase transition from the α phase to the β phase of Cu2 – xSe at ~140°C. It is shown that the superpositions of the subtraction solutions (copper vacancies) and interstitials solutions (copper atoms in interstitial sites), whose proportion is changed as a function of temperature and the deviation from stoichiometry, are in the thermodynamic equilibrium in the copper selenide solid solution at room temperature. The change in the slope of the dependence of the lattice parameter of the powder Cu2 – xSe samples on the composition (0.03 ≤ x ≤ 0.23) in the temperature range 25–350°C enables the suggestion that interstitial copper atom concentration increases with temperature and deviation from stoichiometry.

Abstract —The Cu_2 – _ x Se (0.03 ≤ x ≤ 0.23) powders fabricated by mechanochemical synthesis have been studied by X-ray diffraction. The in situ study has been carried out for the temperature dependences of the lattice parameters, the structures, and the phase compositions of the powders in the temperature range 25–350°C. The powder compositions are shown to differ from the charge compositions and are shifted to lower copper concentrations. The estimation of peak half-widths of the cubic β phase indicates an increase in the structure imperfection after the phase transition from the α phase to the β phase of Cu_2 – _ x Se at ~140°C. It is shown that the superpositions of the subtraction solutions (copper vacancies) and interstitials solutions (copper atoms in interstitial sites), whose proportion is changed as a function of temperature and the deviation from stoichiometry, are in the thermodynamic equilibrium in the copper selenide solid solution at room temperature. The change in the slope of the dependence of the lattice parameter of the powder Cu_2 – _ x Se samples on the composition (0.03 ≤ x ≤ 0.23) in the temperature range 25–350°C enables the suggestion that interstitial copper atom concentration increases with temperature and deviation from stoichiometry.

Выполнены расчеты составов эпитаксиальных слоев, формирующих низкоразмерные гетероструктуры Al x Ga y In 1-x-y As/InP для лазерных диодов с длиной волны излучения 1.55 мкм.При проведении расчетов ставилась задача обеспечения максимальной высоты энергических барьеров для эффективного ограничения носителей заряда в квантовых ямах.Наряду с эффектом размерного квантования энергии свободных носителей заряда в разрешенных зонах, учитывалось влияние упругих напряжений в эпитаксиальных слоях на смещение краев энергетических зон.Показано, что для решения поставленных задач необходимо формирование гетероструктур с напряжениями упругого сжатия в квантовой яме и напряжениями упругого растяжения в барьерных слоях.Предложена структура, включающая барьерный слой Al 0.28 Ga 0.30 In 0.42 As толщиной 110 Å и квантовую яму Al 0.03 Ga 0.23 In 0.74 As в слое толщиной 55 Å со степенями рассогласования параметров кристаллической решетки с подложкой InP -0.8% и +1.4%, соответственно.По результатам расчетной оценки, указанные толщины эпитаксиальных слоев не превышают критических значений, способных привести к образованию дислокаций несоответствия на гетерограницах.

Получены образцы Cu2Se методом механохимического синтеза и компактирования с помощью искрового плазменного спекания и горячего прессования. Методами рентгеновской дифрактометрии и сканирующей электронной микроскопии были исследованы их структура и фазовый состав до и после термообработки. Показано, как изменяется форма и размеры структурных элементов полученных образцов. Исследовано изменение фазового состава селенида меди в интервале температур 25-500oC in situ. DOI: 10.21883/FTP.2017.07.44638.24

Copper selenide is a promising material for power generation in a medium-temperature range 600–1000 K. A number of features of the Cu–Se system, namely, the existence of phase transition in a Cu2Se compound, the high speed of the diffusion of Cu ions, and the high vapor pressure of Se at elevated temperatures, make it necessary to carry out a series of experimental investigations to develop and optimize the methodology for obtaining the bulk material based on copper selenide. The influence of mechanochemical synthesis regimes and subsequent compaction method on the thermoelectric properties and structure of copper selenide is studied. The source material is obtained by mechanochemical synthesis. The methods of hot pressing (HP) and spark plasma synthesis (SPS) are used to obtain the bulk samples. The investigation of the structure and phase composition is performed by the X-ray diffraction and scanning electron microscopy. It is shown that increasing the duration of the mechanochemical synthesis up to 5 h leads to the depletion of copper in powders and to the formation of nonstoichiometric β-phase Cu1.83Se, which persists after SPS. A comparison of the structure and properties of the material obtained by SPS and HP showed that the material obtained by HP has a greater degree of grain defects. The highest thermoelectric efficiency ZT = 1.8 at a temperature of 600°C is achieved for the material obtained by SPS. It is shown that low thermal conductivity is the main factor affecting the value of the thermoelectric efficiency ZT of the studied materials. The difference in the values of thermal conductivity of the materials obtained by different methods is related to the electronic component of thermal conductivity.

Results of studying the formation of InAs quantum dots (QDs) on GaAs(100) substrates by droplet epitaxy using trimethylindium and arsine (AsH3) as precursors are presented. The growth process was carried out at temperatures within 230–400°C in a horizontal reactor for metalorganic vapor phase epitaxy (MOVPE) using high-purity hydrogen as the carrier gas. Data on the influence of process temperature on the QD size and the density of QD array and results of investigation of the low-temperature photoluminescence of obtained samples are presented.

3rd group element nitride based semiconductor compounds are widely used in various optical and electronic devices. One problem in the fabrication of GaN based device heterostructures is the synthesis of p conductivity epitaxial layers. Magnesium is a typical doping impurity for GaN. The choice of optimum doping and thermal activation conditions is of utmost importance for the synthesis of low-Ohmic p-GaN epitaxial layers. The effect of thermal annealing of GaN:Mg layers on acceptor impurity activation has been investigated. Hole concentration increased and mobility decreased with an increase in thermal annealing temperature. The sample annealed at 1000 °C demonstrated the lowest value of resistivity. Rapid thermal annealing (annealing with high heating speed) considerably improved the efficiency of Mg activation in the GaN layers. The optimum time of annealing at 1000 °C has been determined. The hole concentration increased by up to 4 times compared to specimens after conventional annealing.

Исследованы факторы, влияющие на процесс формирования упорядоченного массива квантовых точек InAs капельным методом на поверхности подложки GaAs в условиях гидридной эпитаксии из металлоорганических соединений. С использованием методов квантовой химии выполнен анализ каталитического влияния подложки на пиролиз триметилиндия и арсина. Произведена количественная оценка энергетических параметров, характеризующих процессы пиролиза указанных соединений в гомогенных и гетерогенных условиях. Показана и экспериментально подтверждена возможность существенного снижения температуры процесса формирования квантовых точек InAs рассмотренным методом на подложках GaAs.

An information-calculating system (ICS) that allows computer simulation of processes of semiconductor technology associated with the formation of single crystals and epitaxial heterostructures based on semiconductor AIIIBV compounds was developed. The ICS database covers 9 of AIIIBV compounds and solid solutions based on semiconductor AIIIBV compounds in 18 ternary and 15 four-component systems. The ICS allows solving problems related to the calculation of heterogeneous equilibria in these systems, stability of the formed solid solutions to decay, kinetics of epitaxial growth of heterostructures and non-equilibrium phenomena accompanying heteroepitaxy. In order to create the ICS, we used object-oriented programming Object Windows application programs compiled in the programming language Borland C++ in the Windows environment. Examples of the use of the database for particular semiconductor systems are presented.The above list of problems could be solved with the use of the ICS. The ICS can be used both in research and in educational practice.

The influence of buffer layers formed at different temperatures and ratios of elements of groups V and III (V/III) on crystalline perfection of epitaxial layers AlN grown using the MOS-Hydride Epitaxy Method on the templates α-Al2O3 is considered. It is shown that the most efficient method to increase the structural perfection of epitaxial layers is use of the high-temperature buffer layer on a low V/III ratio. Further improvement of the quality of AlN layers is possible due to the reduction of parasitic reactions between ammonia and trimethylaluminum in the gas phase by means of optimization of the gas flow through the reactor. The specified values of the growth parameters permitted obtaining the AlN layers of the high crystalline perfection (half-width of X-ray swing curves for reflections (0002), (0004) and \((10\bar 13)\) made asec of 50, 97 and 202, respectively) with a good root-mean-square roughness of the surface of 0.7 nm applicable for the creation of instruments based thereon.

Factors affecting the formation of ordered arrays of InAs quantum dots using the drop method on the surface of the GaAs substrate under conditions of MOCVD hydride epitaxy are investigated. The catalytic influence the substrate has on the pyrolysis of trimethylindium and arsine are analyzed by means of quantum chemistry. The energy parameters that characterize the pyrolysis of the investigated compounds under homogeneous and heterogeneous conditions are evaluated quantitatively. The possibility of substantially lowering the temperature of the formation of InAs quantum dots by the considered method on GaAs substrates is shown and confirmed experimentally.

The first stage of formation of InAs/GaAs quantum-dot heterostructures by droplet epitaxy is investigated. Factors influencing the geometrical size and density of arrays of indium nanodrops deposited by trimethylindium pyrolysis on the GaAs(100) substrate are analyzed, and the possibility of using these factors in the process of metal-organic vapor phase epitaxy (MOVPE) are studied. To refine the temperature dependence of the In evaporation rate, a computational experiment taking into account real MOVPE conditions is conducted. An ultimate change in the composition of In droplets contacting the substrate at a high temperature is estimated, and the thickness and composition of crystallizing In-Ga-As solid solution are calculated. It is shown that the size and density of the droplet array to a great extent depend on the crystallochemical structure of the substrate surface and deposition conditions.

Critical thiknesses of formation mismatch dislocations and transition from two dimensional to three dimensional (2D–3D) mode during growth of In x Ga1 − x As/GaAs heterostructures by the Stranski-Krastanow mechanism were estimated using the energy balance model. The maximal magnitudes of those values and the intervals of the composition of solid solutions allowing the growth of defectless quantum dots were obtained.

We have experimentally studied the possibility of obtaining InAs quantum dot arrays on GaAs(100) substrates by droplet-island growth under low-temperature (160–360°C) metalorganic vapor phase epitaxy (MOVPE) conditions. It is established that trimethylindium (In source) exhibits decomposition even at the lower boundary of the indicated temperature interval. The height of In drops formed on the substrate surface was 3–12 nm with a density of ∼(0.4−1.4) × 109 cm−2 depending on the H-MOVPE conditions. In order to retain the dimensions of InAs nanocrystals formed at the subsequent stage, the process should be carried out at an increased rate of arsine supply.

An advanced model for simulation of In segregation phenomena, stress and strain distribution during metal–organic chemical vapor deposition of InGaAs/GaAs(100) quantum well (QW) heterostructures based on representation of boundary gas layer as “quasi-liquid” has been suggested. Elastic energy was taken into account by considering epitaxy as a sequence of growth acts each resulted in the formation of ultrathin imaginary layers. The assumption that elastic influence is not distributed throughout the whole thickness of the substrate but affects only its near-surface layer has been postulated. Results of calculations of In profiles and stress distribution for heterostructures with single and multiple QWs for varied epitaxy conditions are provided. Various options of exploring the developed model for other materials and the limitations of applicability are discussed.

Surface segregation during epitaxial growth of stressed InGaAs/GaAs quantum-well heterostructures significantly distorts the nominal concentration profile of quantum wells. The consideration of the effect for growth conditions and elastic stresses appearing during epitaxy on segregation made it possible to simulate the concentration profile with a high accuracy and to calculate the electroluminescence wavelength of actual InGaAs/GaAs heterostructures with quantum wells. It was shown that the observed effect of the long-wave-length shift for the interband transition wavelength in the important case of heterostructures with two neighboring quantum wells is caused by the influence of elastic stresses during growth.