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The results of a study of liquid photochemical metal-assisted etching of a series of samples of n-type Ga-polar GaN layers grown by molecular-beam epitaxy with nitrogen plasma activation are presented. Under the chosen conditions of the etching process, it is shown that the etching rate depends mainly on the structural properties of the GaN layers, which manifest themselves in the surface morphology, which can be quantitatively characterized by the multifractal parameters Δq (the degree of ordering and symmetry breaking of the structure under study) and Dq (the Rényi dimension, which depends on the thermodynamic formation conditions). A correlation between the values of the multifractal parameters Δq and Dq of the surface structure and the etching rate of Ga-polar GaN layers is established.

A set of structural and spectroscopic methods of diagnostics is used to study the influence of a nanoporous silicon (por-Si) transition layer on the practical implementation and specific features of growth of GaN layers on SiC/por-Si/c-Si templates by molecular-beam epitaxy with the plasma activation of nitrogen. It is shown that a por-Si transition layer introduced into a template, in which a 3C-SiC layer is created by the method of atom substitution, offers unquestionable advantages over standard silicon substrates. Specifically, such an approach makes it possible to lower the level of stresses in the crystal lattice of the epitaxial GaN layer by about 90% and to reduce the fraction of vertical dislocations in the GaN layer. The GaN layer is grown on the surface of the SiC layer, which in turn is on the surface of the SiC/por-Si/c-Si template. It is found for the first time that the use of the SiC/por-Si/c-Si template brings about the formation of a qualitatively more uniform GaN layer free of visible extended defects.

Using a complex of structural and spectroscopic methods of diagnostics, the influence of a nanoporous-silicon (por-Si) transition layer on the optical properties of GaN layers grown on SiC/por-Si/c-Si templates by molecular-beam epitaxy with the plasma activation (MBE PA) of nitrogen is studied. It is shown for the first time that the MBE PA technology of the synthesis of GaN on a virtual SiC/por-Si/c-Si substrate provides a means for producing a GaN film of much higher structural and optical quality at a much lower growth temperature compared to those in similar studies, in which growth on porous Si substrates is demonstrated. The use of a por-Si layer makes it possible to improve the structural and morphological properties of the GaN epitaxial layer and to attain unique optical and electrical characteristics of the layer. The data obtained in the study will serve as an important basis for understanding the foundations of the physics of GaN/SiC/por-Si nanoheterostructures and for promoting their potential use in optoelectronics.

The results of experimental studies of the electronic and photoemission properties of the GaN epitaxial layer grown by molecular beam epitaxy with plasma activation of nitrogen on a SiC/Si (111) substrate are presented. The electronic structure of the GaN surface and the ultrathin Li/GaN interface was first studied in situ under ultrahigh vacuum with various Li coatings. The experiments were carried out using photoelectron spectroscopy with synchrotron radiation in the photon energy range of 75–850 eV. Photoemission spectra in the region of the valence band and surface states and photoemission spectra from N 1s, Ga 3d, and Li 2s core levels are studied with various submonolayer Li coatings. It is found that Li adsorption causes significant changes in the general form of the spectra caused by charge transfer between the Li layer and the lower N and Ga layers. It is established that the GaN surface has predominantly the N polarity. The semiconductor nature of the Li/GaN interface is shown.

The effect of the inversion of polarity in gallium nitride layers from the N-polar GaN layer to the Ga-polar GaN layer was discovered during the sequential growth of GaN films on hybrid SiC/Si(111) substrates by nitrogen plasma-assisted molecular beam epitaxy and chloride–hydride vapor phase epitaxy. A new method has been developed for the formation of crack-free Ga-polar GaN/AlN heterostructures on hybrid SiC/Si(111) substrates. The method includes two stages of growing gallium nitride layers. At the first stage, the transient N-polar GaN layer is grown on the SiC/Si(111) surface by nitrogen plasma-assisted molecular beam epitaxy. At the second stage, two layers are grown on the obtained N-polar GaN layer by chloride–hydride vapor phase epitaxy, namely, the AlN layer and then the GaN layer, which at this stage grows in the Ga-polar orientation. Etching in a KOH solution affects only the N-polar GaN transition layer and leads to its complete removal. This procedure separates the main Ga-polar GaN layer from the SiC/Si(111) substrate completely. The method enables one to grow crack-free and elastically unstressed thick GaN layers and transfer them to substrates of other materials.

Ultrathin epitaxial silicon nitride films were formed on different Si(111) and SiC/Si(111) substrates by nitridation with plasma-activated nitrogen. Photoemission studies of the electronic structure of the SiN and SiCN layers were carried out using photoelectron spectroscopy. The photoemission spectra in the region of the valence band and the core levels of N 1s and Si 2p are studied with synchrotron excitation in the photon energy range of 80–770 eV. The photoelectron spectra of the Si 2p core level for SiN on Si(111) show a characteristic set of components corresponding to the formation of stoichiometric Si3N4. The positions of the intrinsic surface states for the SiN and SiCN films are determined.

The results of studies of photochemical etching processes, which were carried out without applying external voltage, for structures with Ga- and N-polar GaN layers synthesized by molecular-beam epitaxy with the plasma activation of nitrogen are reported. It is shown that the etching rates of layers with different polarities are markedly different. At the same time, the use of gold-based masks instead of titanium-based ones for the etching of GaN layers also provides a means for increasing the rate of layer etching.

Investigation of GaN epitaxial layers on silicon substrates is driven by high potential for fabrication of high efficiency and relatively low-cost electronic devises. Growth process of GaN layers on Si by molecular-beam epitaxy is complicated by mutual diffusion of Si and Ga and differences in thermal expansion coefficients and lattice parameters causing large number of defects. To improve the quality of GaN layers high temperature nitridation of silicon substrates was applied leading to stress relaxation and decrease of diffusion.

The results obtained in a study of the synthesis of n+-GaN layers by plasma-assisted molecular-beam epitaxy on GaN/c-Al2O3 templates are reported. In particular, a method is developed for the pre-epitaxial cleaning of the GaN surfaces of templates to remove foreign atoms. It is shown that, to form GaN layers of comparatively good quality, including those doped with silicon up to ~4.6 × 1019 cm–3, GaN template surfaces should be pre-epitaxially cleaned in a flow of activated nitrogen particles, with the substrate temperature increased from TS = 400 to 600°C and the substrate surface subsequently exposed to a flow of activated nitrogen at a fixed value of TS = 600°C for 1 h. After that the substrate temperature should be raised to TS = 700°C and the GaN surface finally cleaned by means of a procedure for gallium deposition/desorption.

The possibility of synthesizing integrated GaN/por-Si heterostructures by plasma-assisted molecular beam epitaxy without an A1N/Si buffer layer is demonstrated. The beneficial effect of the high-temperature nitridation of a silicon substrate before GaN growth on the crystal quality of the GaN/Si layers is shown. It is established that, to obtain two-dimensional GaN layers on Si(111), it is reasonable to use compliant por-Si substrates and low-temperature GaN seed layers with a 3D morphology synthesized by plasma-assisted molecular beam epitaxy at relatively low substrate temperatures under stoichiometric conditions and upon enrichment with nitrogen. In this case, a self-assembled array of GaN seed nanocolumns with a fairly uniform diameter distribution forms on the por-Si substrate surface. The basic GaN layers, in turn, should be grown at a high temperature under stoichiometric conditions upon enrichment with gallium, upon which the coalescence of nucleated GaN nanocolumns and growth of a continuous two-dimensional GaN layer are observed. The use of compliant Si substrates is a relevant approach for forming GaN-based semiconductor device heterostructures by plasma-assisted molecular beam epitaxy.

The influence of using a buffer sublayer of nanoporous por-Si on the morphological, physical, and structural properties of nanocolumnar InxGa1 –xN structures fabricated by plasma-activated molecular-beam epitaxy on single-crystal Si(111) substrates is shown. Using a set of structural-spectroscopic analytical methods, the electronic structure of the grown heterostructures, morphology, and optical properties are investigated, and the interrelations between them are established. It is shown that the use of a por-Si sublayer makes it possible to attain a more uniform distribution of diameters of InxGa1 –xN nanocolumns and to increase the photoluminescence intensity of the latter.

Using plasma-assisted molecular beam epitaxy (PA MBE) of nitrogen, we obtained integrated heterostructures based on a self-ordered array of GaN nanocolumns on Si substrates with a sufficiently uniform distribution of diameters, which subsequently coalesced into a 2D layer. The use of a ‘compliant’ por-Si substrate for GaN synthesis using PA MBE allowed us to obtain a crack-free GaN layer, prevent the Ga-Si etching process, maintain a sharp smooth Si – GaN interface, and also partially suppress the generation of tensile stresses caused by cooling the heterostructure from growth temperature to room temperature by its relaxation at the Si – GaN nanoporous interface, which had a positive effect on its optical properties in the UV region.

The photoelectric properties of GaN/SiC/Si(111) and GaN/Si(111) heterostructures grown by plasma-assisted molecular-beam epitaxy under the same growth conditions on identical silicon substrates, but with different buffer layers, are experimentally investigated. The GaN/SiC/Si(111) structure is formed on a Si substrate with the SiC buffer layer grown by a new atom-substitution technique and the GaN/Si(111) structure, on a Si substrate subjected to pre-epitaxial plasma nitridation. The significant effect of carbon-vacancy clusters contained in the SiC layer on the growth of the GaN layer and its optical and photoelectric properties is found. It is experimentally established that the GaN/SiC/Si(111) heterostructure has a higher photosensitivity than the GaN/Si(111) heterostructure. In the GaN/SiC/Si(111) heterostructure, the coexistence of two oppositely directed p–n junctions is observed. One p–n junction forms at the SiC/Si interface and the other, at the GaN/SiC interface. It is shown that the occurrence of an electric barrier in the GaN/Si(111) heterostructure at the GaN/Si(111) heterointerface is caused by the formation of a thin silicon-nitride transition layer during pre-epitaxial plasma nitridation of the Si(111) substrate.

Integrated heterostructures exhibiting a nanocolumnar morphology of the InxGa1 –xN film are grown on a single-crystal silicon substrate (c-Si(111)) and a substrate with a nanoporous buffer sublayer (por-Si) by molecular-beam epitaxy with the plasma activation of nitrogen. Using a complex of spectroscopic methods of analysis, it is shown that the growth of InxGa1 –xN nanocolumns on the por-Si buffer layer offer a number of advantages over growth on the c-Si substrate. Raman and ultraviolet spectroscopy data support the inference about the growth of a nanocolumn structure and agree with the previously obtained X-ray diffraction (XRD) data indicative of the strained, unrelaxed state of the InxGa1 –xN layer. The growth of InxGa1 –xN nanocolumns on the por-Si layer positively influences the optical properties of the heterostructures. At the same half-width of the emission line in the photoluminescence spectrum, the emission intensity for the heterostructure sample grown on the por-Si buffer layer is ~25% higher than the emission intensity for the film grown on the c-Si substrate.

Integrated heterostructures exhibiting nanocolumnar morphology of the InxGa1 – xN/Si(111) film are grown on a single-crystal silicon substrate (c-Si(111)) and a substrate with a nanoporous buffer sublayer (por-Si) by molecular-beam epitaxy with the plasma activation of nitrogen. Using a complex of structural and microscopic methods of analysis, it is shown that the growth of InxGa1 – xN nanocolumns on a nanoporous buffer layer offers a number of advantages over growth on c-Si. The por-Si substrate predetermines the preferential orientation of the growth of InxGa1 – xN nanocolumns closer to the Si(111) orientation direction and makes it possible to produce InxGa1 – xN nanocolumns with a higher degree of crystallographic uniformity and with a nanocolumn lateral size of ~40 nm unified over the entire surface. The growth of InxGa1 – xN nanocolumns on a por-Si layer yields a decrease in the strain components exx and ezz and in the density of edge and screw dislocations compared to the corresponding parameters for InxGa1 – xN nanocolumns grown on c-Si. The InxGa1 – xN nanocolumnar layer fabricated on por-Si exhibits a 20% higher charge-carrier concentration compared to the layer grown on c-Si as well as a higher intensity of the photoluminescence quantum yield (+25%).

The growth of single crystalline GaP nucleation and buffer layers on Si substrates by molecular-beam epitaxy is demonstrated. The use of two different regimes of migration-enhanced epitaxy was studied. It was found that p–n junctions can be created due to the interdiffusion during the growth of GaP layer on p-type Si substrate.

The article is devoted to the study of light-emitting heterostructures based on GaP(As,N) dilute nitrides, monolithically grown on silicon substrates by plasma-assisted molecular beam epitaxy. Current-voltage characteristics and electroluminescence spectra of the grown heterostructures are obtained. For the first time, a unique effect is observed in GaP(As,N) dilute nitrides - the appearance of white electroluminescence when a reverse bias is applied. The result was obtained due to the original design of the light-emitting heterostructure and the unique properties of dilute nitride solid solutions.

Using High Resolution X-ray Diffraction (HRXRD) diagnostic techniques the influence of the transition layer of nanoporous silicon on the practical implementation and certain features of the epitaxial growth of GaN layers with the use of molecular beam epitaxy were investigated by means of plasma activation of nitrogen (MBE PA) on the templates of SiC/por-Si/c-Si. For the first time it was shown that introducing of the transition layer of nanoporous silicon in the template of SiC/por-Si/c-Si where the layer of 3C-SiC was obtained by substitution of the atoms had a number of indisputable advantages as compared with conventional silicon substrates. Particularly, such an approach, in fact, enabled a 90% reduction in the level of stresses in the crystalline lattice of the epitaxial GaN layer which was synthesized on SiC surface of SiC/por-Si/c-Si template by means of MBE PA technique as well as to decrease some of vertical dislocations within GaN layer. © 2020 The Authors Russian Science Foundation, RSF The work was executed under support of the grant of Russian Science Foundation 19-72-10007 . Access to KNMF equipment was obtained under the grant of the President of the Russian Federation MD-42.2019.2.

The results of investigations of the effect of the initial conditions (nitridation of the Si(111) substrate, the GaN growth temperature, and the stoichiometry of GaN growth) on the growth kinetics and the GaN/Si(111)-layer polarity under nitrogen-plasma-assisted molecular-beam epitaxy are presented. It is experimentally established that the optimal initial condition for GaN epitaxy on Si(111) substrates is high-temperature nitridation of the Si(111) substrate carried out immediately before GaN growth. It is shown that it is possible to control the polarity of GaN by means of appropriate choice of the growth under conditions with N or Ga enrichment at the initial stage of GaN/Si(111) epitaxy.

The paper focuses on growth of GaN thin films via plasma assisted molecular beam epitaxy on SiC/Si(111) substrate formed by atom-by-atom substitution method. A comparison with GaN film grown in the same process directly on Si(111) substrate is performed. The films were studied by ellipsometry, electron diffraction and Raman spectroscopy. The results of these measurements are used to compare polarity of the films, crystalline properties, quality and residual elastic stresses in GaN films grown on Si and SiC/Si substrates. It is shown that SiC buffer layer has a positive effect on the structural quality of growing GaN thin films. It was found that use of SiC/Si(111) substrate leads to formation of N-polar film, whereas Ga-polar film is formed on Si(111).

In this work, the AlN/Si(111) epitaxial structures grown consistently by plasma assisted molecular beam epitaxy (PA MBE) and hydride vapour phase epitaxy (HVPE) methods were studied. The PA MBE AlN buffer layers were synthesized via coalescence overgrowth of self-catalyzed AlN nanocolumns on Si(111) substrates and were used as templates for further HVPE growth of thick AlN layer. It was shown that described approaches can be used to obtain AlN layers with sufficiently smooth morphology. It was found that HVPE AlN inherited crystallographic polarity of the AlN layer grown by PA MBE. It was demonstrated that the etching of such AlN/Si(111) epitaxial structures results in partial separation of the AlN epilayers from the Si(111) substrate and allows to form suspended structures. Moreover, the avoidance of surface damage and backside overetching was achieved by use thin Cr film as surface protective coating and by increasing the layer thickness accordingly.

Two different approaches for the etching of the gallium nitride epitaxial layers grown on Si(111) substrates by plasma-assisted molecular beam epitaxy have been elaborated. It is demonstrated that anisotropic etch profiles can be achieved by both photoenhanced wet chemical etching and reactive plasma-chemical etching methods. Moreover, it is shown, that the photoenhanced wet chemical etching allows to remove GaN layer without damaging silicon substrate.

The GaN/Si(111) epitaxial structures were synthesized by coalescence overgrowth of GaN nanocolumns using the plasma-assisted molecular beam epitaxy (PA-MBE) technique. Such epitaxial structures can be used as a buffer layer for obtaining high quality GaN epilayers. Structural, electrical and chemical properties of these samples were studied. It was demonstrated that KOH etching of the grown GaN/Si(111) samples results in the separation of the GaN epilayer from the substrate.

The AlN/Si(111) epitaxial structures were synthesized by coalescence overgrowth of AlN nanocolumns using PA MBE technique. Such epitaxial structures can be used as a buffer layer for obtaining high quality AlN and GaN layers. Structural, electrical and chemical properties of these samples were studied. For the first time it was demonstrated that the etching of the obtained type of AlN/Si(111) structures in KOH can become a promising method for obtaining high quality free-standing AlN and GaN.

The dependence of the crystallographic polarity of GaN epitaxial layers produced by nitrogen plasma-enhanced molecular-beam epitaxy on Si(111) substrates on the nitridation parameters and initial growth conditions has been studied. A rapid procedure for determining the polarity of GaN epitaxial layers was developed. It was found experimentally that the nitridation parameters of the silicon substrate have no effect on the polarity of a GaN layer. It was shown that the substrate temperature in the stage of nucleation of a GaN epitaxial layer is one of the factors determining its polarity.

Using the complexes of structural and spectroscopic diagnostic techniques, we investigated the influence of the layer of nanoporous silicon on the practical implementation and certain features of the epitaxial growth of GaN layers with the use of MBE PA on the templates of SiC/por-Si/c-Si. For the first time, the layer of nanoporous silicon has been introduced in the template of SiC/por-Si/c-Si where the layer of 3C-SiC was obtained by the substitution of the atoms; this had a number of indisputable advantages as compared to conventional silicon substrates. In particular, the abovementioned approach enabled a 90% reduction in the stress levels in the crystalline lattice of GaN layer that was synthesised on the SiC surface of the SiC/por-Si/c-Si template; it also decreased some of the vertical dislocations within the GaN layer. We also found that the use of the SiC/por-Si/c-Si template resulted in the formation of a more uniform (by its quality) GaN layer without any visible extensive defects. As a result, this enabled us to attain unique optical and electro-physical characteristics for the hybrid heteroepitaxial GaN/SiC structures. The obtained data will be very important for understanding the basic physics of nanoheterostructures of GaN/SiC/por-Si, thus promoting their potential applications in optoelectronics.

Gallium nitride (GaN) thin films grown on Si(111) substrates via plasma-assisted molecular beam epitaxy were investigated. The morphology of GaN films was studied by scanning electron microscopy. It was found that GaN films at nanoscale contain a large amount of cavities. The Raman measurements of GaN/Si(111) system were performed and showed that the position of the GaN E2 (TO) band is close to that of unstrained GaN. We proposed a stress relaxation mechanism to explain the low stress state of GaN films.

The n+-GaN epilayers were synthesised by PA MBE on the SiO2 patterned GaN/c-Al2O3 templates, grown by MOCVD. Formation of the polycrystalline GaN atop of the SiO2 mask during PA MBE was observed. It was found that macroscopic voids at the interface polycrystalline GaN/SiO2/n-GaN template appeared during the PA MBE process. The polycrystalline GaN film was completely removed by etching in hot aqueous KOH solution. Hall measurements have shown that the value of electron concentration in n+-GaN contact layer is about ne∼4.6×1019 cm-3.

The growth of monolith GaAsP/Si dual-junction solar cells on Si substrates by molecular-beam epitaxy is demonstrated. The technological method for the formation of a highly doped tunnel p+/n+ junction was developed. An obvious increase in the value of the open-circuit voltage indicating the contribution of the top-junction in the total open-circuit voltage monolithic dual-junction solar cells was found.

The results of studies of the growth kinetics of AlN layers during molecular beam epitaxy with the plasma activation of nitrogen using Si (111) substrates are presented. The possibility of the growth of individual AlN/Si (111) nanocolumns using growth conditions with enrichment of the surface with metal near the formation mode of Al drops, at a substrate temperature close to maximal, during molecular beam epitaxy with the plasma activation of nitrogen (Ts ≈ 850°C) is shown. The possibility of growing smooth AlN layers on a nanocolumnar AlN/Si (111) buffer with the use of Ts ≈ 750°C and growth conditions providing enrichment with metal is shown.

We have performed micro-photoluminescence (µ-PL) mapping of InGaN films with thickness up to 300 nm with a large gradient of In concentration in a lateral direction (from 10% to 40%), grown by plasma-assisted molecular beam epitaxy atop a 1.8-µm-thick GaN() buffer deposited on a c-Al2O3 substrate. The µ-PL spectra measured at various points with different average composition show almost identical emission bands with fixed wavelength ranges: 490-540 nm (green band), 550-590 nm (orange band), and 600-660 nm (red band). This behavior implies emergence of at least three phases with fixed In contents, which are nearly independent of the average film composition and the variation of the growth temperature. The variation of the average composition of the InGaN ternary alloy results in redistribution of the band intensities that can be explained by redistribution of the relative volumes of the spatially separated phases. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present a comparative study of three samples with a single Al0.3Ga0.7N/Al0.4Ga0.6N quantum well (QW) grown by plasma-assisted molecular beam epitaxy on c -sapphire substrates with an AlN buffer deposited under different Al/N flux ratios. We show by means of transmission electron microscopy that strong N-rich growth conditions result in a three-dimensional morphology that is inherited by the QW. As a result, the QW is corrugated on the size scale of the QW photoluminescence (PL) wavelength (∼300 nm). The Al-rich conditions lead to a two-dimensional growth and formation of a plane QW with flat interfaces. The PL line in the corrugated QW is 5 times more intensive and shifted toward larger energies by ∼200 meV, as compared with the plane QW. The superior emission properties are explained by simultaneous action of several factors such as suppression of the quantum-confined Stark effect, enhanced carrier localization, and improved efficiency of light extraction. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Low-temperature (

The electric fields in Al0.3Ga0.7N/Al0.4Ga0.6N quantum wells are estimated. The quantum wells are grown by plasma-assisted molecular-beam epitaxy with plasma activation of nitrogen. The three-dimensional and planar modes of buffer layer growth are used. The transition to the three-dimensional mode of growth yields a substantial increase in the photoluminescence intensity of the quantum wells and a shift of the photoluminescence line to shorter wavelengths. These effects are attributed to the fact that, because of the extra three-dimensional localization of charge carriers in the quantum-well layer, the quantum-confined Stark effect relaxes. The effect of localization is supposedly due to spontaneous composition fluctuations formed in the AlGaN alloy and enhanced by the three-dimensional growth.

Solar-blind UV photodetectors based on photocathodes are among the important applications of heterostructures based on group III metal nitride semiconductors. Related investigations are most frequently devoted to photocathodes with p-GaN active regions characterized by a long-wavelength sensitivity threshold at 360 nm. Since the detected radiation is mostly concentrated in the spectral range below 240–290 nm, corresponding displacement of the long-wavelength sensitivity threshold of photodetectors by using photocathodes with p-AlGaN active regions is a topical task. We present preliminary results on manufacturing photocathodes with a p-AlxGa1 − xN (x = 0.1 and 0.3) active region (possessing a long-wavelength sensitivity threshold at 330 and 300 nm, respectively).

Comparative study of growth kinetics of the Al x Ga 1-x N (x=0-1) layers grown by plasma-assisted molecular beam epitaxy (PA MBE) under different growth conditions (group III to activated nitrogen and Al to Ga flux ratios) is presented. The strong influence of elastic stress on the surface morphology, growth rate and Al content in Al x Ga 1 -x N (x= 0-1) layers is most pronounced for the Al x Ga 1- x N films with high Al-content grown atop of the 2D-AlN buffer layer at near the unity flux ratio F III /F N ~1. The use of strong Ga-rich growth conditions with F III /F N ~ 1.6-2 for the growth of Al x Ga 1- x N/2D-AlN with high Al-content (x > 0.25) allows one to reduce the strain effect as well as provide smooth surface morphology and precise control of Al content in the Al x Ga 1-x N (x=0-1) layers by employing a simple ratio x=F Al F N .

We have demonstrated optically pumped room-temperature pulse lasing at 300.4 nm from an AlGaN-based multiple-quantum-well (MQW) structure grown by plasma-assisted molecular beam epitaxy on a c-sapphire substrate. The lasing was achieved at the threshold peak power of similar to 12 MW/cm(2). The MQW structure involved AlGaN/AlN short-period super-lattices to decrease the threading dislocation densities from 10(11) down to 10(9)-10(10) cm(-2). Studies of time-resolved photoluminescence (TRPL) spectra and cw PL temperature dependences (10-300K) of different MQW structures, as well as numerical calculations of the optical gain and confinement in the laser structure allowed us to conclude about the optimum design of AlGaN-based MQW structures for the lower threshold UV lasing.

The effects of GaN nanocolumn arrays and a thin SixNy layer, used as buffer layers, on the morphology of GaN epitaxial layers are investigated. Two types of samples with different buffer layers were synthesized by PA-MBE. The morphology of the samples was characterized by SEM. The crystalline quality of the samples was assessed by XRD. The possibility of synthesis of continuous crystalline GaN layers on Si(111) substrates without the addition of other materials such as aluminum nitride was demonstrated.

The results of comparative studies of the growth kinetics of the GaN layers of different polarity during ammonia molecular beam epitaxy and plasma-assisted molecular beam epitaxy (PA MBE) of nitrogen with the use of sapphire substrates and GaN(000 $$ \bar 1 $$ )/c-Al2O3 templates grown by gas-phase epitaxy from metalorganic compounds are presented. The possibility is shown of obtaining the GaN layers with an atomically smooth surface during molecular beam epitaxy with plasma activation of nitrogen. For this purpose, it is suggested to carry out the growth in conditions enriched with metal near the mode of formation of the Ga drops at a temperature close to the decomposition temperature of GaN (TS ≈ 760°C). The conclusion is made that an increase in the growth temperature positively affects the structural, optical, and electrical properties of the GaN (000 $$ \bar 1 $$ ) layers. A high quality of the GaN (0001) films grown by the PA MBE method at a low temperature of ∼700°C on the GaN/c-Al2O3 templates is shown.

Al-rich AlGaN layers and quantum well (QW) structures with a reasonable structural quality have been grown by plasma-assisted molecular beam epitaxy (PA-MBE) under metal-rich stoichiometric conditions directly on c-sapphire. The bowing parameter of 1.1 eV for the compositional dependence of AlGaN band gap energy has been determined using an electron-probe microanalysis, Raman spectroscopy and optical transmission spectroscopy. A successful application of a sub-monolayer digital-alloying (SMDA) technique in PA-MBE for fabrication of AlGaN-based multiple QW structures, including deep-UV MQW light-emitting diodes, has been demonstrated for the first time. These structures exhibit both photo- and electroluminescence in the spectral range of 300–320 nm at room temperature.

Features of plasma-assisted molecular-beam epitaxy of AlGaN compounds at relatively low temperatures of the substrate (no higher than 740°C) and various stoichiometric conditions for growth of the nitrogen- and metal-enriched layers are studied. Discrete submonolayer epitaxy for formation of quantum wells and n-type blocking layers without varying the fluxes of components was used for the first time in the case of molecular- beam epitaxy with plasma activation of nitrogen for the nanostructures with the Al x Ga1 − x N/Al y Ga1 − y N quantum wells. Structural and optical properties of the Al x Ga1 − x N layers in the entire range of compositions (x = 0–1) and nanostructures based on these layers are studied; these studies indicate that there is photoluminescence at room temperature with minimum wavelength of 230 nm. Based on the analysis of the photoluminescence spectra for bulk layers and nanoheterostructures and their temperature dependences, it is concluded that there are localized states in quantum wells. Using the metal-enriched layers grown on the c-Al2O3 substrates, heterostructures for light-emitting diodes with Al x Ga1 − x N/Al y Ga1 − y N quantum wells (x = 0.4–0.5, y = x + 0.15) were obtained and demonstrated electroluminescence in the ultraviolet region of the spectrum at the wavelength of 320 nm.

The processes leading to the formation of a spatially nonuniform distribution of indium in the InxGa1 − x N layers with x = 0−0.6 grown by molecular beam epitaxy with plasma activation of nitrogen at relatively low growth temperatures (590–630°C) are studied. It is found that at low values of x < 0.1, the growth proceeds pseudomorphically at least to a thickness of 70 nm, and these layers are characterized by a high uniformity of the In distribution, which confirms their thermodynamic stability. Upon increasing x up to ∼0.3, the signs of a nonuniform In distribution are observed, which is associated with the stress relaxation facilitating the development of phase separation. It is shown that layers with In distribution of lower uniformity feature more intense photoluminescence in the energy range 2.0–2.5 eV. For the layers with x = 0.6, complete phase separation is observed with the formation of several phases with a wide range of compositions, including the region in the vicinity of the InN binary compound.