The internal quantum efficiency of GaAs/AlGaAs- and InGaAs/AlGaAs-heterostructures for infrared light emitter diodes has been determined. The influence of the growth conditions of heterostructures grown by the molecular beam epitaxy and post-growth annealing on the quantum efficiency of heterostructures has been investigated. It has been shown that it is possible to increase the quantum luminescence efficiency of the studied heterostructures up to 75-80% at the average power by the combined optimization of these processes. Keywords: GaAs/AlGaAs and InGaAs/AlGaAs heterostructures, internal quantum exit, photoluminescence, molecular-beam epitaxy.

In the present work, the low-fluence nonablating femtosecond laser irradiation (λ = 800 nm) of the GeO2 layer with Ge nanoclusters protected by SiO2 layers is studied by different types of microscopy (optical microscopy, atomic force microscopy, and scanning and transmittance electron microscopy) and Raman spectroscopy. After the laser modification, the multilayer thickness increased by 6%–29% depending on the laser fluence. It was found that the laser fluence of ∼40 mJ/cm2 was the optimal value for observing the swelling effect and was below the ablation threshold. Irradiation at this fluence led the Ge nanoclusters to decrease in size from 5–8 to ∼2 nm and crystallize, while the GeO2 matrix expanded due to the formation of GeO bubbles. The fabrication mechanism of the novel type of nanofoam consisting of a glassy matrix, cavities filled with gas, and semiconductor nanocrystals with reduced size dispersion is discussed. Presumably, this effect is associated with the selective absorption of IR (800 nm) laser radiation by Ge nanoclusters.

Методами атомно-силовой микроскопии и динамической вторично-ионной масс-спектрометрии были исследованы структурные свойства и структурное совершенство выращенных методом молекулярно-лучевой эпитаксии из аммиака Al x Ga 1-x N/AlN/Al 2 O 3 гетероструктур с высокой концентрацией кремния в слоях Al x Ga 1-x N : Si. Показано, что в случае, если буферные слои AlN металлической полярности содержат инверсионные домены азотной полярности, при последующем росте слоев Al x Ga 1-x N : Si инверсионные домены не прорастают до поверхности, а меняют азотную полярность на металлическую. На месте инверсионных доменов AlN растут уширяющиеся колонны Al x Ga 1-x N металлической полярности, которые срастаются с окружающей их матрицей металической полярности в однородную пленку. Толщина, на которой происходит полное срастание, увеличивается с увеличением содержания Al в слоях. Ключевые слова: A 3 -нитриды, инверсионные домены, структурные дефекты, аммиачная-МЛЭ.

The effect of different degrees of the sapphire surface nitridation process completion on the AlN buffer layer morphology has been studied. It was found that ~85% completion of the AlN crystalline phase formation promotes the growth of a two dimensional AlN buffer layer with a smooth surface morphology, regardless of the substrate temperature and ammonia flux. In contrast, during the AlN nucleation layer formation as a result of weak or excessive sapphire nitridation, a polycrystalline or three-dimensional AlN structures with a high density of inversion domains, respectively, were formed. Using independent methods of X-ray photoelectron spectroscopy and infrared spectroscopy of surface polaritons, the thickness of the AlN nucleation layer was determined at ~85% degree of the nitridation process completion, which amounted to ~1 monolayer.

The effect of different degrees of the sapphire surface nitridation process completion on the AlN buffer layer morphology has been studied. It was found that ~85% completion of the AlN crystalline phase formation promotes the growth of a two dimensional AlN buffer layer with a smooth surface morphology, regardless of the substrate temperature and ammonia flux. In contrast, during the AlN nucleation layer formation as a result of weak or excessive sapphire nitridation, a polycrystalline or three-dimensional AlN structures with a high density of inversion domains, respectively, were formed. Using independent methods of X-ray photoelectron spectroscopy and infrared spectroscopy of surface polaritons, the thickness of the AlN nucleation layer was determined at ~85% degree of the nitridation process completion, which amounted to ~1 monolayer. Keywords: ammonia molecular beam epitaxy, AlN, sapphire, reflection high-energy electron diffraction, nitridation, inversion domains, X-ray photoelectron spectroscopy, surface polaritons.

In this study, an atomically clean and structurally ordered Bi2Se3 (0001) surface is obtained without molecular beams and vacuum cleaving. It is shown that the chemical treatment of Bi2Se3 (0001) in an anhydrous solution of hydrogen chloride in isopropyl alcohol leads to the removal of native oxides and enrichment of the surface with an elemental selenium layer. Heating in an ultrahigh vacuum at a temperature of 170°C leads to the desorption of the elemental selenium layer from the surface and the formation of a structurally ordered unreconstructed Bi2Se3 (0001) surface with the linear dispersion law.

The structural properties and crystal quality of AlxGa1 ‒ xN/AlN/Al2O3 heterostructures grown by ammonia-assisted molecular-beam epitaxy with a high silicon concentration in the AlxGa1 ‒ xN:Si layers are studied by atomic force microscopy and dynamic secondary-ion mass spectrometry. It is shown that if AlN buffer layers of metal polarity contain inversion domains of nitrogen polarity, during subsequent growth of the AlxGa1 ‒ xN:Si layers, inversion domains do not grow to the surface, but change their nitrogen polarity for metal polarity. At the place of AlN inversion domains, broadening AlxGa1 ‒ xN columns of metal polarity grow, which coalesce in a homogeneous film with the Me-polar matrix surrounding them. The thickness corresponding to complete intergrowth increases with the Al content in the layers.

An atomically clean and structurally ordered surface of the CdTe layer of a (013)-oriented GaAs/ZnTe/CdTe substrate after storage in air is obtained by treatment in isopropyl alcohol saturated with hydrochloric-acid vapors, with subsequent thermal annealing in ultrahigh vacuum. It is shown that chemical treatment of the CdTe surface results in the removal of native oxides and in enrichment of the surface with an elemental Te layer. During heating in vacuum, two stages of change in the state of the surface (at ~125 and ≤250°C) are observed. At the temperature T > 250°C, elemental tellurium is desorbed, and a Te-stabilized (1 × 1) CdTe(013) structure is formed.

The paper presents a technology for preparing the silicon Si(111) substrates surface for the III-nitride compounds epitaxial growth by molecular beam epitaxy technique. The technology includes the following stages: chemical surface pretreatment by the Shiraki method, bakeout in the preliminary annealing chamber, the substrates heating in the growth chamber in order to obtain an atomically clean and ordered silicon surface, the samples cooling with subsequent registration of the (7x7) superstructure. The search for surface preparation conditions was carried out using (1) high-energy electron diffraction, which in situ revealed carbon contamination in the form of silicon carbide compounds formed during high-temperature heating of silicon, and (2) high-resolution optical microscopy, which recorded dislocation slip lines caused by a temperature gradient in sample heating process. For uniform heating/cooling of the substrate and suppression of the process of generation and slip of dislocations that appear at the edges of the substrate, the substrate mounting arrangement was modified. It has been demonstrated that the surface of Si(111) substrates prepared using the proposed technology is suitable for the epitaxial growth of III-nitride structures.

A comparative study of the structural properties of GaN layers and the electrophysical parameters of 2DEG in AlGaN/GaN heterostructures grown by ammonia molecular beam epitaxy on sapphire and silicon substrates using identical buffer layer designs has been carried out. It is demonstrated that GaN layers grown under the same growth conditions have the similar surface morphology, regardless of the substrate material. It is shown that the dislocation density of compressed GaN layers grown on sapphire substrates up to 5 times lower than in crack-free and stretched GaN layers grown on silicon substrates. The measured values of electron mobility in heterostructures with 2DEG grown on sapphire substrates are higher by 30% than on silicon substrates (-1600 cm(2)/V x s and-1200 cm2/V x s).

Quick label-free virus screening and highly sensitive analytical tools/techniques are becoming extremely important in a pandemic. In this study, we developed a biosensing device based on the silicon nanoribbon multichannel and dielectrophoretic controlled sensors functionalized with SARS-CoV-2 spike antibodies for the use as a platform for the detection and studding of properties of viruses and their protein components. Replicatively defective viral particles based on vesicular stomatitis viruses and HIV-1 were used as carrier molecules to deliver the target SARS-CoV-2 spike S-proteins to sensory elements. It was shown that fully CMOS-compatible nanoribbon sensors have the subattomolar sensitivity and dynamic range of 4 orders. Specific interaction between S-proteins and antibodies leads to the accumulation of the negative charge on the sensor surface. Nonspecific interactions of the viral particles lead to the positive charge accumulation. It was shown that dielectrophoretic controlled sensors allow to estimate the effective charge of the single virus at the sensor surface and separate it from the charge associated with the binding of target proteins with the sensor surface.

In this work, atomically clean and structurally ordered surface of CdTe epitaxial layer after storage in air by treatment in isopropyl alcohol saturated with vapors of hydrochloric acid, and further temperature heating in an ultrahigh vacuum, was obtained. CdTe surface chemical treatment results in the removal of native oxides and surface enrichment with elemental tellurium. Heating in vacuum leads to the tellurium desorption and the appearance of a Te-stabilized CdTe surface. During heating in vacuum, two stages of surface state change are observed (~125°С and ≤250°С). At Т>250°С, elemental tellurium is desorbed and a Te-stabilized structure (1x1) CdTe(013) is formed.

The InAs areas formation on the surface of InP (001) substrates annealed in an arsenic flux in an ultra-high vacuum was determined by scanning electron microscopy and atomic force microscopy. It is shown that the InAs areas are distributed non-uniformly over the surface and have an elongated shape predominantly along the [11̅0] direction. The height and density of InAs areas increases with an increase in the annealing temperature.

Определен внутренний квантовый выход люминесценции GaAs/AlGaAs- и InGaAs/AlGaAs-гетероструктур для инфракрасных светодиодов. Исследовано влияние ростовых условий гетероструктур, выращенных методом молекулярно-лучевой эпитаксии и пост-ростового отжига на квантовый выход гетероструктур. Показано, что совокупной оптимизацией данных процессов удается повысить квантовый выход люминесценции исследуемых гетероструктур до 75-80% при умеренной мощности накачки. Ключевые слова: гетероструктуры, кельвиновская зондовая микроскопия, молекулярно-лучевая эпитаксия.

It is demonstrated that it is possible to use the ammonia molecular beam epitaxy for growing structurally perfect high-ohmic GaN layers which allow generating SiN/Al(Ga)N/GaN heterostructures for transistors with a high mobility of electrons. The growth conditions are determined for GaN layers with smooth surface morphology (with a mean-squared deviation of $${\sim}$$ 2 nm) appropriate for creating sharp heteroboundaries. The possibility of improving the crystalline perfection of GaN layer due to the use of buffer high-temperature AlN layer (with the growth temperature above 940 $${}^{\circ}$$ C) is demonstrated. It was shown that in situ surface passivation of Al(Ga)N/GaN heterostructures by the ultrathin SiN layer allows generating normally closed transistors with unprecedented low values of the current collapse ( $${\sim}1\%$$ ).

Бинарные соединения Bi2Te3, Bi2Se3 и Sb2Te3 являются классическими примерами трехмерных (3D) топологических изоляторов (ТИ). Одной из возможных областей практического применения этих материалов является детектирование терагерцового излучения [1]. Однако, халькогениды висмута и сурьмы – это материалы с высокой проводимостью, обусловленной легированием собственными дефектами, что затрудняет исследования поверхностных топологических состояний. Так, в Bi2Te3 и Sb2Te3 избыток металла занимает узлы решетки Te и действует как легирующая примесь p-типа. Поэтому, чтобы осуществить исследования транспортных свойств ТИ, связанные с их топологическими поверхностными состояниями, необходимо уменьшить вклад объемных состояний в проводимость. Одним из вариантов решения данной проблемы является рост твёрдых растворов тройных и четверных соединений. Так в работе [2] было показано, что электрофизические свойства соединения (BixSb1-х)2(SeyTe1-y)3 (BSTS) зависят от содержания компонент.

Titanium oxynitride (TiOxNy) coatings increase the bio- and hemocompatibility of stainless steel and Co-Cr vascular stents, possibly by directly releasing NO. Herein, to examine the applicability of this approach to nitinol (NiTi) devices, we coated NiTi samples with TiOx or TiOxNy by reactive magnetron sputtering using different reaction gas compositions and bias voltages. One side of the samples was preliminarily abraded, while the other remained in its original state. Samples morphology, composition and structure were studied by atomic force microscopy (AFM), X-ray diffraction (XRD) and field emission scanning electron microscopy (FE SEM). We investigated how various types of TiOx and TiOxNy coatings interact with EA.hy926 endothelial cells. None of the tested samples exhibited cytotoxicity, and an N2:O2 ratio of 3:1 regardless of the bias voltage was found to be optimal for NO production and cell adhesion, spreading, and viability, which was ascribed to a cumulative positive effect of the composition and nanoroughness of TiOxNy coatings formed under these conditions. Thus, the deposition of TiOxNy coatings was concluded to be a promising strategy of increasing the biocompatibility of NiTi stents.

The phase transitions during the oxidation of polycrystalline tin (beta-Sn) were studied. The intense photo-luminescence from SnO was observed in the annealing temperature range of 300-400 degrees C. An increase in the annealing temperature led to a sharp decrease in photoluminescence. It is associated with the phase transition of SnO to SnO2. Two approaches were proposed for obtaining the dual-band material based on tin oxides and GeSiSn compounds. Using the Sn-rich nanoislands grown on the vapor-liquid-solid (VLS) mechanism, the nanoislands having SnO(x) in their upper part, and the SiSn solid solution under SnO(x) were obtained after annealing. Furthermore, the growth technology of the dual-band material, which included tin oxides on top of a GeSiSn/Si multiple quantum well (MQW) structure, was developed. Tin oxides demonstrated the photo-luminescence signal in the visible region, whereas the SiSn solid solution in nanoislands and GeSiSn/Si multiple quantum well structure showed the photoluminescence signal in the infrared range.

The article presents how the understanding of the fundamental processes of self-organization and morphological transformations of the atomically clean Si(111) surface as a result of the study using in situ ultrahigh vacuum reflection electron microscopy can be applied to metrology. The method of high-resolution transmission electron microscopy is used to show that the native oxide formed on the Si(111) surface in atmospheric conditions replicates the atomic step height with high accuracy. The techniques for creating vertical measures in the range 0.31–31 nm with an error of less than 0.05 nm in the entire measurement range are developed on this basis. It is shown that it is possible to create extremely wide atomically smooth surfaces (up to 230 $$\mu$$ m) and use them as reference mirrors in interferometric microscopes. Crystal samples containing a certain number of monoatomic steps and atomically smooth surface areas are included in the State Secondary Reference Standard as a measure of angstrom height and angstrom flatness.

Surface morphology evolution of flat GaAs epitaxial layers grown on mesa structured substrates is studied under annealing in the presence of a saturated Ga-As melt. At high temperatures T 700 degrees C, when the annealing conditions are shifted from the equilibrium towards sublimation, the initially flat surface roughens by unwinding spiral monatomic steps, which are induced by screw dislocations. This process leads to the formation of "inverted pyramid" spiral pits. Along with the spiral pits, the roughening consists in multilayer island formation on terraces, at the surface spots where the sublimation is inhibited. The mechanism of island formation is reproduced in the Monte Carlo simulation. The obtained data allowed us to estimate the relative undersaturation of -0.015 and Ga adatom diffusion length of 15 nm at T = 750 degrees C. Annealing at higher temperature T = 775 degrees C resulted in a peculiar "vortex"-like surface morphology, which consists in deep spiral pits covering the major part of the surface area.