This work describes the synthesis characteristics of GaN layers using plasma-assisted molecular beam epitaxy on Si (111) substrates, without employing the substrate nitridation procedure or forming an intermediate Al-containing layer. It was found that in GaN layers grown directly on the Si substrate, after passivating its surface with Ga atoms, the residual stress values remain consistent across different layers of the epitaxial film. Additionally, GaN exhibits a high packing density of crystallites on the surface, indicated by a smaller block size, which is associated with a high density of dislocations at the grain boundaries. The introduction of an additional indium flux as a surfactant during the growth of the GaN layer results in the formation of InxGa1-xN solid solution regions on the surface of an amorphous SixNy sublayer sublayer, which is formed between between the nanocolumns during the growth of of the nucleation layer. In this case, scenario, gradient distribution of residual stresses stresses is observed the depth of the GaN film film, decreasing it approaches the surface). surface. The results demonstrate using proposed technology it enables the growth of films with stable optical properties, properties without the formation of cracks in the epitaxial film.

This study considers the growth characteristics of nickel oxide NiO films using DC magnetron sputtering. The hysteresis transition process between sputtering from poisoned and clean Ni target as a function of discharge power was determined. The structure, atomic composition, and optical and electrical properties of NiO films for two modes of sputtering (with low and high discharge power, respectively) have been investigated. It is demonstrated that sputtering parameters have a fundamental effect on both the formation of structure and atomic composition and on the trend of their modification using temperature annealing. The results obtained for each of the sputtering modes can be applied to the development of devices based on catalytic reactions as well as on their semiconductor properties.

The electronic structure of the clean AlN surface and the ultrathin K/AlN interface has been studied in situ by synchrotron-based photoelectron spectroscopy using the photon energies in the range of 100-650 eV. The effect of K adsorption was studied. Changes in the valence band and in the Al 2p, N 1s, and K 3p core levels spectra have been investigated using K submonolayer deposition. Modification of the surface electronic structure of the AlN caused by K adsorption is found to originate from the local interaction of N surface atoms and K adatoms. As a results the suppression of intrinsic surface state and appearance of a new induced state are observed. It was found the K-induced electron redistribution effect that causes the positive energy shift of N 1s surface peak and increasing N-ionicity. Keywords: III-nitrides, electronic structure, surface states, metal-III-nitride interfaces, photoelectron spectroscopy.

Abstract Nickel oxide is a promising material for transparent electronics applications. This semiconductor demonstrates the possibility of modifying its physical properties depending on the method of growth and subsequent processing. Here the effects of the discharge power are reported during reactive dc magnetron sputtering, as well as the modes of subsequent annealing of NiO films, on their structural, electrical, and optical properties. NiO films are annealed at various temperatures both in an oxygen‐containing environment and under vacuum conditions. Deposited NiO films have a polycrystalline structure with a preferred orientation (200) for the low discharge power mode and (111) for the high discharge power mode. However, obtained NiO films exhibit crystallinity improvement after annealing. The presence of both Ni2+ and Ni3+ oxidation states in the deposited films is found. In addition, it is shown that the relative carrier concentration (Ni3+/Ni2+ peak area ratio) can be controlled by choosing the NiO film preparation mode. The trend in this ratio corresponds to the trend in film conductivity and the number of free‐charge carriers. The deposited films are semitransparent, and the estimated optical bandgap of NiO is in the range from 3.50 to 3.74 eV.

Nickel oxide semiconductor is a good p -type material for fabricating a p - n -heterojunction with n -type GaN semiconductor. The p -NiO/ n -GaN heterojunction, which produces a type II band bias, has significant prospects for creating photosensitive devices. Herein, it is shown that a selective ultraviolet photodetector can be created based on this heterojunction. p -NiO films were formed using magnetron sputtering onto n -doped GaN epitaxial layers grown by plasma assisted molecular beam epitaxy. The structural, optical, and electronic properties of the formed nickel oxide films were studied. A mechanism for reducing dislocation density and conductivity and increasing transparency due to film annealing is proposed. It has been established that the current-voltage characteristics of the p -NiO/ n -GaN heterojunction are typical for diode structures and show selective sensitivity to ultraviolet radiation. The band model and sensitivity of the fabricated ultraviolet photodiode were evaluated. The photosensitivity at zero voltage was 3.11 mA/W, the quantum yield was 0.011, and the detection ability was 8.69 x 10 9 Jones. The work shows the potential of using the p -NiO/ n -GaN heterojunction to create ultraviolet photodetectors.

The electronic structure of the epitaxial GaN/Si(111) layers and the Li/GaN/Si(111) interface with a monolayer Li coverage has been studied in situ under ultrahigh vacuum conditions. The experiments were carried out using photo electron spectroscopy with synchrotron radiation in the photon energy range 75–850 eV. The photoemission spectra in the valence band and the core levels of Ga 3d, N 1s, and Li 1s are studied for the monolayer Li coating. It is found that Li adsorption causes a significant decrease in the intensity of the photoemission line of the intrinsic surface state and the appearance of an induced surface state due to charge transfer between the adsorbed Li layer and surface Ga atoms. It has been found that the GaN/Si(111) surface has predominantly Ga polarity. The Li/GaN/Si(111) interface has a semiconductor character.

An approach to create ohmic contacts to GaN layers without using the high-temperature annealing procedure is described in the paper. The results of comparative studies of structural, morphological, optical, and electrical properties of undoped GaN and silicon-doped n-GaN and n+-GaN doped contact layers are presented. The contact layer technology can be successfully realized using a plasma-assisted molecular beam epitaxy (PA MBE) setup of industrial type, where due to characteristic design features, the growth of nitride AIIIN compounds occurs using small streams of activated nitrogen, which significantly limits the possibility of varying the technological parameters. For the first time it is demonstrated that using the proposed technology for the creation of post-grown GaN, nGaN and n+-GaN contact layers to GaN/c-Al2O3 virtual substrates in Ga-enriched conditions of epitaxial PA MBE growth at relatively low temperatures Ts = 700oC an effective filtration of dislocations threading from the buffer GaN layer of the virtual substrate formed by MOCVD can be realized. Calculations of in-plane epsilon xx and out-of-plane epsilon zz deformations, as well as residual biaxial stresses based on Xray diffraction and Raman microspectroscopy data indicate at high structural quality of the formed contact layer regardless of the silicon doping level. At the same time PA MBE contact layers GaN, n-GaN and n+-GaN demonstrate close optical properties (refractive index and photoluminescence) in a wide range (400-850 nm), as well as minimal influence of defects associated with the formation of silicon clusters at high doping levels. The contact resistance reduced to the pad width determined using the transmission line method for the structure with n+-GaN contact layer was of -0.11 Ohm*mm and -0.5 Ohm*mm for n-GaN. Note that electrophysical characteristics of n-GaN and n+-GaN contact layers do not degrade under high-dose exposure of highenergy X-ray irradiation. The technique developed in our work to create ohmic contacts to GaN layers, as well as the obtained experimental results, have important implications for understanding the physics of AIIIN nanoheterostructures and will contribute to their potential applications in their fabrication.

The effect of sodium adsorption on a gold film deposited on a tungsten substrate was studied. The deposition of Na atoms onto a thin film of gold on tungsten leads to a change in the spectra of the valence band and the core levels of gold and tungsten. An analysis of the spectra showed that the sodium atoms in the surface layer are in a neutral state, and the diffusion of sodium atoms deep into the gold film leads to the formation of the NaxAuy intermetallic compound. Heating a gold film with the formed NaxAuy intermetallic compound at a temperature 640 K leads to partial desorption of sodium and gold atoms from the surface layer of the NaxAuy intermetallic compound.

The electronic structure of ultrathin Cs/Bi2Se3 interfaces has been studied by photo electron spectroscopy using synchrotron radiation. The experiments were carried out in situ in ultrahigh vacuum with submonolayer Cs coverages on Bi2Se3 samples. It was found that the adsorption of Cs causes changes in the core level spectra of Bi 4f, Bi 5d, Se 3d. It has been established that Cs atoms are adsorbed predominantly on Bi atoms in the upper surface layer. The states of the valence band were studied for a clean Bi2Se3 surface and for the Cs/Bi2Se3 interface. Near the Fermi level, 2D topological states have been found. Two induced surface states appear in the region of the valence band upon adsorption of Cs.

This paper investigates the optical and electrical properties of ITO films for their application as a transparent contact electrode to NiO films. The films were fabricated by magnetron sputtering at various parameters of the discharge power and oxygen content in the working gas mixture. Structural analysis showed an increase in the crystallinity of the films during their subsequent annealing. The films demonstrate high conductivity and transparency with an absorption edge higher than that of NiO films. The results of the study show a high potential for using ITO films to create a transparent electrode to NiO layers.

Fabrication of electric contacts is one of the most important stages in the electronic devices manufacturing process. Recently, considerable attention is paid to non-alloyed ohmic contact studies, although the more conventional approach usually involves contact formation by rapid thermal annealing of the sputtered metallization. In this work the contact resistance of alloyed (Ti/Al/Ni/Au and Ti/Al) and non-alloyed (Yb/Au) ohmic contacts to n-GaN epitaxial films is compared. Ti/Al/Ni/Au alloyed ohmic contacts have the lowest resistance. However, it is found that the contact resistance values for non-alloyed Yb/Au and alloyed Ti/Al contacts are similar. Thus, low-resistance non-alloyed Yb/Au-based ohmic contacts to n-GaN are demonstrated.

The electronic structure of the epitaxial GaN/Si(111) layers and the Li/GaN/Si(111) interface with a monolayer Li coverage has been studied in situ under ultrahigh vacuum conditions. The experiments were carried out using photoelectron spectroscopy with synchrotron radiation in the photon energy range 75-850 eV. The photoemission spectra in the valence band and the core levels of Ga 3d, N 1s, and Li 1s are studied for the monolayer Li coating. It is found that Li adsorption causes a significant decrease in the intensity of the photoemission line of the intrinsic surface state and the appearance of an induced surface state due to charge transfer between the adsorbed Li layer and surface Ga atoms. It has been found that the GaN/Si(111) surface has predominantly Ga polarity. The Li/GaN/Si(111) interface has a semiconductor character. Keywords: III-nitrides, electronic structure, metal-GaN interface, photoelectron spectroscopy.

n situ photoelectron spectroscopy studies have been carried out in ultrahigh vacuum of the electronic structure of a 2D Au film deposited on a surface W with a natural oxide, before and after adsorption of Na atoms. The spectra of photoemission from the valence band and core levels of Au 4f, W 4f and Na 2p were studied under synchrotron excitation in the photon energy range of 120-300 eV. The investigated 2D Au film with a thickness of 0.83 nm has a valence band close to the valence band of the massive sample. The diffusion of Na atoms deep into the gold film was not detected, which indicates the layered growth of the 2D Au film. Two states have been found: Nadelta+ and Na+, which exist even with a 0.15 sodium coating of the monolayer, which indicates the formation of Na islands and single adsorption of Na atoms. The density functional method is used to calculate the electronic structure of a 2D Au layer without and with adsorbed Na. It is established that the adsorption of Na atoms in the pit or bridge position is preferable. It is found that the adsorption of Na leads to the reconstruction of the surface.

Problems of the growth of nanoscale columnar AlxGa1-xN/AlN heterostructures on hybrid substrates involving porous silicon and silicon carbide layers by molecular beam epitaxy technique with plasma-activated nitrogen are discussed in this study. The epitaxial growth of nanoscale columnar AlxGa1-xN/AlN heterostructure is shown to be specified by the layer of silicon carbide, which is formed by atomic substitution technique, and a porous silicon sublayer predetermines the oriented growth of SiC. The performed complex of structural-spectroscopic analysis demonstrated that epitaxial growth of the nuclear AlN layer on all types of the substrates in N-enriched conditions resulted in the formation of AlxGa1-xN/AlN heterostructures with Ga-polar surface. At the same time it was found that the layer of ordered AlxGa1-xN alloy was formed only on the hybrid SiC/porSi/cSi substrate. The layer of AlxGa1-xN on the substrates of cSi and porSi/cSi is present in the state of disordered alloy with an excess content of gallium atoms. Nanocolumns of AlxGa1-xN/AlN grown on the hybrid SiC/porSi/cSi substrate have two types of preferential azimuthal orientation that affects not only their structural and optical properties but also the value of elastic deformation in the heterostructure nanoscale layers. For the first time, azimuthal dependence of intensity of E1(TO) and E2high photon modes was detected in the Raman spectra. The observed periodicity angle in micro-Raman scattering coincides with the characteristic swivel of nanoscale columns of AlxGa1-xN/AlN around c-axis according to the data of XRD pole figure measurements. Results obtained in our work show promising capabilities in the use of SiC/porSi/сSi substrates for integration of silicon technology and technology of synthesis of the nanoscale columnar AlxGa1-xN heterostructures by molecular-beam epitaxy with plasma-activated nitrogen.

The growth of nanoscale columnar AlxGa1-xN/AlN heterostructures on the surface of silicon substrates using plasma-activated nitrogen molecular-beam epitaxy was investigated in this work. Silicon substrates include atomic-smooth cSi substrate, Si substrate with a transition layer of porous silicon porSi/cSi and a hybrid substrate involving a silicon carbide layer grown with matched substitution of the atoms on the surface of porous silicon SiC/porSi/cSi. A complex analysis performed using a set of structural and spectroscopic techniques demonstrated that the epitaxial growth of the nuclear AlN layer on all types of the substrates in a N-enriched environment resulted in the formation of AlxGa1-xN/AlN heterostructures with a Ga-polar surface, which was realized only on the SiC/porSi/cSi substrate. The layer of AlxGa1-xN on cSi and porSi/cSi substrates was in the state of disordered alloy with an excess of gallium atom content. It was shown that a great difference in the lattice parameters of a substrate–film pair resulted not only in the appearance of a number of various defects but also in a considerable effect on the chemical process of the formation of the alloys, in our case, the AlxGa1-xN alloy. It was shown that nanoscale columns of AlxGa1-xN formed on SiC/porSi/cSi substrate were inclined relative to the c-axis, which was connected with the features of the formation of a SiC layer by the matched substitution of the atoms on the porous Si substrate, resulting in the formation of the inclined (111) SiC facets at the boundary of the (111) Si surface and pores in Si. Optical studies of the grown samples demonstrated that the optical band-to-band transition for the AlxGa1-xN alloy with Eg = 3.99 eVB was observed only for the heterostructure grown on the SiC/porSi/cSi substrate. A qualitative model is proposed to explain the difference in the formation of AlxGa1-xN layers on the substrates of cSi, porSi/cSi and SiC/porSi/cSi. The results obtained in our work demonstrate the availability of using SiC/porSi/cSi substrates for the integration of silicon technology and that used for the synthesis of nanoscale columnar AlxGa1-xN heterostructures using plasma-activated molecular-beam epitaxy with a nitrogen source.

The electronic structure of ultrathin Cs/Bi2Se3 interfaces has been studied by photoelectron spectroscopy using synchrotron radiation. The experiments were carried out in situ in an ultrahigh vacuum with submonolayer Cs coverages on Bi2Se3 samples. It was found that the adsorption of Cs causes changes in the spectra of the core levels of Bi 4f, Bi 5d, and Se 3d. It has been established that Cs atoms are adsorbed predominantly on Bi atoms in the upper surface layer. The states of the valence band are studied for a clean Bi2Se3 surface and for the Cs/Bi2Se3 interface. Near the Fermi level, 2D topological states have been found. Two induced surface states appear in the region of the valence band upon adsorption of Cs.

We carried out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen plasma activation on a hybrid substrate containing layers of silicon carbide and porous silicon. Using X-ray diffractometry, Raman and photoluminescence spectroscopy, it is shown that thin films formed on a hybrid substrate have minimal residual stresses and intense photoluminescence.

The electronic structure of a gold film deposited on W was studied during the adsorption of sodium atoms. An analysis of the photoemission spectra from the valence band and core levels of Au 4f and Na 2p upon synchrotron excitation in the photon energy range of 80–600 eV showed that Na adsorption leads to the formation of NaxAuy intermetallic compounds of various stoichiometry under the Na monolayer.

Photoelectron spectroscopy was used to study the electronic structure in situ in an ultrahigh vacuum before and after the adsorption of sodium atoms on the surface of tungsten oxidized at an oxygen pressure of 1 Torr and a temperature of 950 K. The photoemission spectra from the valence band and the W 4f, O 2s, and Na 2p core states were studied under synchrotron excitation in the photon energy range 80-600 eV. It is found that a tungsten oxide film is formed containing various tungsten oxides with an oxidation state of 6+ to 4+. The deposition of a 1.1 monolayer of sodium atoms on the surface of oxidized tungsten leads to the reduction of the W6+ states to W4+ and the reaction with oxygen in the hydroxyl composition, which is reflected in the change in the spectrum of the W 4f and O 2s core states. It is shown that the cathodoluminescence spectrum is associated with the luminescence of tungsten oxide. Keywords: adsorption, sodium, tungsten oxides, photoelectron spectroscopy, cathodoluminescence.