This report presents the results of an experiment to obtain and characterization of quasi-bulk monocrystal epitaxial ε-Ga2O3/GaN heterostructures which contain V-defects at the interface. The significance of this work is due to an active search for ways to develop device-heterostructures for deep-ultraviolet optoelectronics and for HEMT transistors in high-frequency and high-power electronics. One such solution is epitaxial growth of a thick ε-Ga2O3 layer on templates with GaN epitaxial layer to form ε-Ga2O3/GaN heterostructure. The ε-Ga2O3 is characterized by a wide band gap and high spontaneous polarization. The Ga2O3 layer was grown by chloride-hydride vapor-phase epitaxy on pre-prepared GaN/AlN/3C-SiC/Si structures. As the reactor was cooled to room temperature, the Ga2O3/GaN heterostructure (with an AlN buffer layer) spontaneously detached from the SiC/Si substrate due to the balance of the layer thermal expansion coefficients. The surface morphology of the gallium oxide layer and the cross-section of the interface in the Ga2O3/GaN heterostructures were studied using scanning electron microscopy with TESCAN MIRA 3. The phase composition and crystal quality of the Ga2O3/GaN heterostructures were studied by X-ray diffraction on the DRON-8 diffractometer of JSC Bourevestnik. Transmission spectra of the heterostructures were obtained by spectrophotometry using an integrating sphere. This paper demonstrates the epitaxial growth of Ga2O3/GaN heterostructures through chloride-hydride vapor phase epitaxy and the possibility of detaching epitaxial layers from the template. Scanning electron microscopy studies of cross-section have shown that the Ga2O3/GaN heterostructures contain a quasi-bulk gallium oxide with a thickness of about 100 microns. Additionally, it was also shown that the heterostructures contained V-defects on the GaN growth surface, with the Ga2O3 layer grow over V-defects. X-ray diffraction study revealed that the formed heterostructure contains ε-Ga2O3 monocrystal layer, and the fell width at half maximum intensity of the diffraction reflection curve 0,0,10 is 1.8 degrees, which indicates satisfactory quality for thick epitaxial layer. The results of the study openup the possibility to develop templates and substrates for epitaxial growth of wide-bandgap semiconductor materials. Optimization of the growth modes and geometry of such heterostructures with a thick ε-Ga2O3 layer is a promising area for further research.

Photocatalysts are currently widely used in various research and industrial fields, from water and air purification to solar energy, from self-cleaning surfaces to wearable biosensors and electronic devices. Among semiconductors, the growing interest is attracted to gallium oxide, especially beta-Ga2O3, due to the unique physical, chemical (especially acid-resistance), physical-chemical, photochemical properties, and redox potential. These photocatalysts can be used not only as suspended mixture, but also in the form of films, nanoparticles, and nanofibers. The last one is more challenging due to the high level of surface-to-volume ratio, porousness, air and water permeability, and excellent morphological and physical-mechanical properties. Moreover, electrospinning techniques, in comparison with fabrication of nanoparticles, allow to obtain photocatalytic devices without usage of additional carrying base, which simplify the industrial process. However, to date there are limited publications related to the Ga2O3 electrospun nanofibers. The aim of this review is to summarize current results of gallium oxide electrospun nanofibers preparation. Special attention is given to the technological parameters of the electrospinning, the polymer solution receipts, and the properties of such nanomaterials and its potential application. Despite the limited number of publications related to Ga2O3 fibers fabrications, that data collected in this review article demonstrate great potential for practical applications.

The work presents the results of the experiments on annealing in air of bulk crystals of gallium oxide grown in Ar+O-2 and CO(2 )atmospheres at a temperature of 1400 degrees C. The annealing time was 5 hours; the time to reach the temperature was 3.5 hours; the cooling time was 20 hours. Annealed samples show increasing of transmission in infrared area of electromagnetic spectrum and decreasing of width of X-ray rocking curve which means the reduction of the number of defects in crystals. Full width at half maximum of rocking curve for annealed samples was almost the same for both atmospheres: FWHMa a = 84 arcsec for sample grown in Ar+O-2 atmosphere and FWHMa a = 80 arcsec for sample grown in CO2, which means that after annealing, the quality of the samples became comparable, despite the initial difference.

The work demonstrates the synthesis of thin films of β-(AlxGa1–x)2O3 by spray pyrolysis method. Temperature conditions for sol synthesis are determined to obtain thin films with a specified content of aluminum. The films are studied by scanning electron microscopy, energy-dispersive X-ray spectroscopy and optical spectroscopy. The aluminum content in the fabricated β-(AlxGa1–x)2O3 films is about 3.6 at.%. The optical band gap of the films is determined as 5.0 eV.

Proton irradiation of β-Ga2O3 crystals has been established to lead to a significant increase in the amount of Cr3+ ions being active in luminescence. Using angle-resolved luminescence, the features of the spectra of Cr3+ ions were studied. The high sensitivity of photoluminescence spectra and the related selection rules to the local symmetry of Cr3+ ions in the β-Ga2O3 matrix has been found. The results obtained indicate the potential possibility of using β-Ga2O3 crystals as optical dosimeters of proton irradiation.

The article studies the influence of aluminum on the lattice parameters and the unit cell volume of the binary solid solution β-(AlxGa1–x)2O3. The aluminum content is determined by energy-dispersive X-ray spectroscopy. The lattice parameter values are calculated using X-ray diffractometry data. The diffraction patterns show peak broadening and shift to higher angles with increasing aluminum content. It is shown that when the aluminum fraction x changes from 0 to 0.25, the lattice parameters decrease linearly. This is consistent with Vegard’s law for solid solutions. The decrease in cell volume is physically related to the fact that aluminum has a smaller ionic radius than gallium, and the Al–O bond length is shorter than Ga–O one.

The article presents the results of the study of the mechanical properties and defect structure of gallium oxide (Ga2O3) by using the piezoelectric composite oscillator technique. Bulk samples of the Ga2O3 beta phase in the form of single crystals and their intergrowths were obtained by growth from a melt with a shaper (Stepanov technique). The research involved studying the dependences of the longitudinal elastic modulus and the damping of elastic vibrations at a frequency of 100 kHz on the strain amplitude. Changes in the elastic and microplastic properties of the samples at different temperatures were attributed to possible relaxation phenomena in the structure of the material. Studying the defect structure in samples of pure and doped Ga2O3 is necessary to improve the technology for the production of large single crystals. The fundamental questions in this area are the influence of defects on the anisotropy of electrical conductivity, band structure, and other functional properties of the resulting semiconductor material. The purpose of this article is to establish the features of sample preparation, research, and interpretation of the results obtained by the piezoelectric composite oscillator technique for gallium oxide samples. In the studied samples, the first longitudinal vibration mode was excited, which corresponded to a length of about 27 mm and a small cross-section of the sample. The temperature dependences in the region of low and high strain amplitudes were determined separately. The crystalline quality of the prepared samples was assessed by X-ray diffraction with the analysis of the rocking curve. The value of Young’s modulus obtained along the growth axis (crystalline orientation <010>) in Ga2O3 crystals E≈260 GPa is in line with the results of previous studies. Relaxation peaks corresponding to various dislocation interactions were found on the temperature dependences of internal friction at a temperature of 280 K

This work is devoted to the study of the luminescence inhomogeneity nature of bulk (GaxAl1–x)2O3 samples grown by the Czochralski method. In the study of sample cleavages by the local cathodoluminescence method, regions with different luminescence were observed. To determine the cathodoluminescence contrast nature, we studied the uniformity of the aluminum distribution, the surface topography, and compared the luminescence spectra and the kinetics of emission bands for different regions of the sample. Also, to determine the luminescence bands nature, the crystal was annealed in air at 1000°C. This made it possible to observe the change in luminescence for the same region of the sample. Based on the studies performed, it was concluded that inhomogeneous luminescence is associated with the distribution of point defects. Upon annealing in air, the transformation of nonradiative recombination centers into luminescent centers was observed.

В статье приводятся результаты исследования механических свойств и дефектной структуры оксида галлия (Ga2O3) при помощи метода составного пьезоэлектрического осциллятора. Объёмные образцы бета фазы Ga2O3 в виде монокристаллов и их сростков были получены при помощи роста из расплава с формообразователем (метод Степанова). Исследовались зависимости модуля продольной упругости и затухания упругих колебаний на частоте 100 кГц от амплитуды деформации. Изменения упругих и микропластических свойств образцов при различной температуре были сопоставлены с возможными релаксационными явлениями в структуре материала. Изучение дефектной структуры в образцах чистого и легированного Ga2O3 необходимо для совершенствования технологии получения монокристаллов большого размера. Фундаментальными вопросами в данной области являются влияние дефектов на анизотропию электропроводности, зонную структуру и другие функциональные свойства получаемого полупроводникового материала. Цель данной статьи в установлении особенностей подготовки образцов, проведении исследований и интерпретации результатов, полученных методом составного пьезоэлектрического осциллятора для образцов оксида галлия. В исследуемых образцах возбуждалась первая продольная мода колебаний, что соответствовало длине около 27 мм и малому поперечному сечению образца. Отдельно определялись температурные зависимости в области низких и высоких амплитуд деформаций. Для оценки кристаллического совершенства образцов, подготовленных для исследований, использовалась рентгеновская дифракция с анализом кривой качания

Bulk crystals of β-Ga2O3 were successfully grown by the edge-defined film-fed growth method. The crystalline quality of the obtained crystals was analyzed by the method of x-ray diffractometry. The full width at half maximum of the rocking curve was about 72 arcsec. The optical bandgap was determined by analyzing the optical transmission spectra and amounted to 4.7 eV. The hot disk method was used to obtain the thermal conductivity of the sample along the [001] direction in the temperature range from 30 to 120 °C. The maximum value of thermal conductivity obtained at 30 °C was 9.25 W/(m K).

Bulk crystals of [Formula: see text]-Ga 2 O 3 were successfully grown by the EFG (Stepanov) method. Analysis of the material using an X-ray diffraction showed the high crystalline quality of the obtained crystals. However, when determining the elemental composition by the Energy Dispersive X-ray Spectroscopy (EDS) method, a deviation of the crystal composition from a stoichiometric one was found and a lack of oxygen was detected. Indirectly, this indicates the non-optimal composition of the atmosphere in the growth zone. The origin of this deviation of the composition can be oxygen vacancies in the bulk of the crystal. However, the absorption spectrum does not contain peaks characteristic for oxygen vacancies in gallium oxide. An analysis of the optical transmission spectra made it possible to estimate the optical bandgap of the grown gallium oxide samples, which was 4.7 eV.

β-Ga2O3 thin films were obtained by the sol-gel method on sapphire and quartz substrates, as well as on Cu-O buffer layers. It was shown that the sol-gel method allowed to obtain β-Ga2O3 thin films with good optical and structural properties by using X-ray diffraction, scanning electron microscopy and optical spectroscopy. The energy of the optical band gap of Ga2O3 films calculated by the Tauc plot varied from 4.39 to 4.59 eV.

Optical system consisting of single-mode optical fiber and p-i-n photodiode semiconductor chip with InGaAs active layer was investigated. Considered photodetector module has responsivity in 1.3–1.6 μm. The problem of optical power loss due to inaccurate matching between the optical fiber and the active medium of photodiode in photodetector modules is investigated; resolving the power loss problem will lead to an increase in the spectral photosensitivity and external quantum efficiency of the photodetector module. Optimization of optical fiber coupling with semiconductor chip was implemented in Zemax® software with built-in Levenberg–Marquardt algorithm. Also, numerical calculations of the influence of the transverse and longitudinal displacement on optical coupling efficiency in the photodetector module were carried out. The optical system of photodetector module based on standard metal can package was built in Zemax® software. Optimal distances between elements of the photodetector module were calculated, and maximum efficiency of 93.1 % optical coupling between single-mode fiber and photodiode aperture was achieved. The necessary sensitivity of linear micro translators used during the assembly of photodetector modules was determined to ensure the alignment of optical elements with coupling efficiency more than 90 %. The results of this work can be used in the design of photodetector modules. The proposed solutions can be relatively easily modified to create photodetector modules of other spectral ranges.

Bulk (Al x Ga 1− x ) 2 O 3 crystals with an Al fraction x in the range from 0.0 to 0.23 were successfully grown by the Czochralski method. An increase in the band gap from 4.7 to 5.1 eV with the rise of the Al content was demonstrated by analyzing optical transmission spectra. The crystal quality of the obtained samples was characterized by X-ray diffractometry. The appearance of the crystal’s mosaic blockness was found for the Al fraction x above 0.05.

In this paper we study wire contacts made of varied materials (Ag, Au, Cu) and microwelding methods at contact pads with different coatings — immersion gold, galvanic gold, galvanic silver. We present the results of bonding pull-off/shear force testing and compare results of various wire contacts technological operation.

This work is devoted to the study of the luminescence inhomogeneity nature of bulk (GaxAl1-x)2O3 samples grown by the Czochralski method. In the study of sample cleavages by the local cathodoluminescence method, regions with different luminescence were observed. To determine the cathodoluminescence contrast nature, we studied the uniformity of the aluminum distribution, the surface topography, and compared the luminescence spectra and the kinetics of emission bands for different regions of the sample. Also, to determine the luminescence bands nature, the crystal was annealed in air at 1000oC. This made it possible to observe the change in luminescence for the same region of the sample. Based on the studies performed, it was concluded that inhomogeneous luminescence is associated with the distribution of point defects. Upon annealing in air, the transformation of nonradiative recombination centers into luminescent centers was observed. Keywords: gallium oxide, luminescence, point defects.

Работа посвящена исследованиям природы неоднородности люминесценции объемных образцов (GaxAl1-x)2O3, выращенных методом Чохральского. При исследовании сколов образцов методом локальной катодолюминесценции наблюдались области с различной люминесценцией. Для определения природы катодолюминесцентного контраста были проведены исследования однородности распределения алюминия, топографии поверхности, сравнение спектров люминесценции и кинетики полос излучения для различных областей образца. Также для определения природы полос люминесценции был проведен отжиг кристалла на воздухе при 1000oC. Это позволило наблюдать изменение люминесценции для того же участка образца. На основании проведенных исследований был сделан вывод о том, что неоднородная люминесценция связана с распределением точечных дефектов. При отжиге на воздухе наблюдалась трансформация центров безызлучательной рекомбинации в люминесцентные центры. Ключевые слова: оксид галлия, люминесценция, точечные дефекты.

Continuous monitoring of patient’s state in intensive care units is crucial for displaying critical conditions and identifying signs of clear consciousness. Traditional monitoring on a bedside monitor represents digital value on the screen and has several shortcomings. The observer’s perception of digital information is limited by visual acuity and affects the speed of decision-making. The radio frequency range is increasingly overloaded with the development of Internet of Things devices. It leads to numerous errors in the transmitted data. The developed system is aimed at the comprehensive elimination of the shortcomings through available means. An understandable visualization system is preferred for prompt recognition of changes in the patient’s state, increasing the speed of perception of the observer, and receiving information in the form of a data set. A data transmission system via optical wireless communication is relevant for duplicative channel for displaying and eliminating the shortcomings of systems operating in the radio frequency range. The system being developed is universal and can be used in a wide range of professional fields. In particular, if the use of the radio frequency range is limited and the stability of the data transmission channel to electromagnetic interference is essential.

In this article, we report on fabricating thin solid films of gallium oxide by the spray-pyrolysis method. This method allows obtaining uniform thin films more easily compared with other sol-gel methods like spin-coating or dip-coating. In the experiment, sol concentrations were experimentally selected for further deposition on substrates. Morphology and chemical composition of the deposited films were studied by Scanning Electron Microscopy and Energy-Dispersive X-ray spectroscopy, respectively. The structural properties of the films were analyzed by X-ray diffraction method. The band gap of the Ga2O3 films was estimated by analyzing the optical transmission spectra and was 4.87 eV. The quality and homogeneity of the obtained coatings are evaluated.

Bulk β-Ga 2 O 3 samples grown by the Czochralski method are studied. Based on the studies of the absorbed current dynamics and the cathodoluminescence, it is shown that there is a localization of charges of both signs in the sample. The electron localization is demonstrated to lead to a substantial decrease in cathodoluminescence intensity.