Equilibrium distributions of misfit dislocation density along the growth direction of metamorphic buffer layers InxAl1-xAs/GaAs with maximum In content xmax ≥ 0.77 and different non-linear graded composition profiles (x ∝ z1/n) are calculated. The effect of the initial In composition (xmin) of InxAl1-xAs buffer layer with convex-graded (n = 2) composition profile on misfit dislocation density as well as amount of residual stresses at its top part is considered. Using computational approach, it was shown that a dislocation-free region is formed under thin tensile-strained GaAs layer (1–10 nm) inserted into InAlAs metamorphic buffer layer, which agrees with experimental data obtained early by transmission electron microscopy. Novel non-linear graded composition profile of metamorphic buffer layer has been proposed, which results in twice reduction of misfit dislocation density as compared to the convex-graded one. In addition, equilibrium distributions of misfit dislocation density in the HEMT heterostructures with two-dimensional electron channel In0.75Ga0.25As/In0.75Al0.25As, which are based on InxAl1-xAs/GaAs metamorphic buffer layer of various designs, are calculated. The values of inverse steps (∆), representing the difference between the maximum In content of InxAl1-xAs (xmax) and In content of In0.75Al0.25As virtual substrate, at which relaxation of the elastic strains in 2D channel In0.75Ga0.25As/In0.75Al0.25As doesn’t occur, are calculated for metamorphic buffer layers InxAl1-xAs with convex-graded and optimized non-linear graded composition profiles.

We present the results of terahertz generation studies under excitation via femtosecond lasers pulses epitaxial films of InAs, which were synthesized on semi-insulating and highly doped GaAs substrates. It is shown that a terahertz emitter based on epitaxial InAs film grown on a heavily doped GaAs n-type substrate, has the same terahertz generation efficiency as the InAs-film emitter grown on a semi-isolating GaAs substrate, but it has a significantly better spectral resolution, which is mainly determined by the parameters of the optical delay line and the femtosecond laser’s stability.

На основе представлений о дислокационно-динамической диффузии атомов и молекул среды в приповерхностные слои твердых тел при их деформации рассмотрено влияние предварительной деформации меди и железа в среде жидкого азота, способствующей интенсивному проникновению азота в приповерхностные слои металлов, на положение максимумов зависимости скорости десорбции молекул воды от температуры. Обнаружено смещение максимумов в сторону более высоких температур в результате предварительной деформации. Произведено сравнение различных способов разделения пиков на кривых десорбции воды и оценены энергии активации процессов десорбции в низко- и высокотемпературных областях, а также высказаны предположения о причинах влияния деформации в жидком азоте на характеристики десорбции молекул воды при нагревании. Ключевые слова: десорбция молекул воды, деформация в среде азота, дислокационно-динамическая диффузия.

Here we report on computing of the distribution of the equilibrium misfit dislocation density ρ(z) as well as the elastic strain ε(z) along the grow direction for metamorphic buffer layer InAlAs/GaAs(001) with high In content (x ≤ 0.87) and different design of composition profile: step-, linear- and convex-graded. For the computation, an approach based on the iterative finding the system total energy minimum have been used. It was shown, that the significant difference between different types of the buffer layer is observed for the ρ(z) distribution rather than for ε(z). In contrast to traditionally used step- and linear-graded metamorphic buffer layers, which are characterized by homogenous spreading of misfit dislocations, the main part of such dislocations in the convex-graded composition profile is concentrated at the bottom part of the buffer layer near to heterointerface InAlAs/GaAs, and the dislocation density drop by more than one order of magnitude along the layer thickness reaching near the surface the minimal value among the buffer types. Despite the fact, that the significant effect of interaction between misfit dislocations is not taken into account in the computation, the results obtained allowed one to determine the main features of the ρ(z) and ε(z) distributions in the different InAlAs metamorphic buffer layers, which were previously obtained experimentally. Thus, such an approach can be effectively utilized for the development of the metamorphic heterostructure based devices.

Рассмотрено влияние среды гелия при дроблении порошка цемента и прокатке поликристаллического алюминия на количество и кинетику десорбции молекул воды с поверхности этих материалов при нагревании с постоянной скоростью. Произведено разделение пиков на кривых десорбции воды, и показано влияние среды гелия при разрушении (дроблении) и деформировании (прокатке) на характеристики десорбции. Оценены энергии активации процессов десорбции воды в различных температурных областях и их изменение при разрушении и деформации материалов в гелии и на воздухе. Высказано предположение о замещении атомами гелия вакантных для адсорбции молекул воды мест на вновь образующихся участках поверхности тел, подвергнутых механическому воздействию, и о проникновении адсорбированных атомов и молекул среды в приповерхностный слой материала по механизму дислокационно-динамической диффузии. Ключевые слова: десорбция молекул воды, среда гелия, дробление цемента, прокатка алюминия.

AbstractThe results of optimization of the design and growth conditions of an In_ x Al_1– x As metamorphic buffer layer with a high In content ( x = 0.05–0.83) grown via MBE on GaAs(001) substrates with the purpose of optimizing its surface morphological characteristics and structural properties and lowering the surface density of threading dislocations. The lowest surface-pattern roughness RMS = 2.3 nm (on an area of 10 × 10 μm) and density of threading dislocations of 5 × 10^7 cm^–2 are found in the samples with a convex-graded metamorphic buffer layer.

Поступило в Редакцию 11 мая 2017 г

Evidence is obtained for the first time for penetration of helium atoms into amorphous films subjected to tensile strain in liquid helium at T = 0,5-4,2 K. The amounts of helium entering the amorphous films and plots of its extraction are obtained and the helium extraction rate peaks corresponding to the crystallisation and melting points of these materials are revealed. It is shown that helium penetrates into amorphous films in the region of plastic shears while being practically absent in the non-strained parts of the samples

Mass-spectra of the release of3He and 4He have been obtained for highand technical purity titanium deformed in tension in liquid 3He (T = 1K) and 4He from the titanium oxide, subjected to a dispersion in gaseous 4He at 293 K has also been investigated. A drastic increase of the amount of He has been found in deformed titanium samples and in the powder of titanium oxide after dispersion. Mass-spectra of the He evolution exhibit one or two peaks in a temperature domain T = 160-6200C. The phenomenon of Dislocation Dynamic Diffusion penetration of He atoms along moving dislocation into material being deformed is used to account for the experimental results.