In this work, we study the morphology, composition and optical properties of AlGaN epilayers grown by plasma-assisted molecular beam epitaxy on the AlN buffer layer which was performed on regular Si substrate and compliant Si substrate with a preformed buffer porous silicon layer (por-Si) and carbonized porous layer(SiC/por-Si). The AlGaN layers formed on the por-Si buffer revealed a 15% higher intensity of photoluminescence spectra in visible range in comparison with ones formed on regular Si substrate.

tangar77@mail.ru Abstract. We present an experimental study of multilayer porous silicon formed by elec-trochemical etching. Special emphasis is placed on effects that arise from a stepwise decrease in the current density while maintaining the total etching time. In order to provide a fully understanding of the morphology of the surface, we used scanning electron and atomic force microscopy. X-ray reflectivity was used to assess the porosity of porous layers. It was found that a stepwise decrease in the current density leads to the formation of a two-layer structure without changing the porosity of the base bottom layer. However, the porosity of the top layer can be varied over a wide range, which directly affects the photoluminescence of the samples. Our results show how the sample production conditions affect the fine tuning of the surface layer morphology of multilayer porous silicon.

Addition of the second magneto-plasma-dynamical (MPD) stage allows significant increase of the thrust, the thrust-to-power ratio (TPR) and the efficiency of the micro-cathode arc thruster (μCAT) [1] . Previously, we studied the effect of the magnetic field source and configuration, and the shape of the second-stage electrode on the performance of the μCAT-MPD thruster [1] - [3] . Since the second-stage electrode is the main factor in the onset of the vacuum arc leading to the performance improvement [1] , it seems that the distance between the two stages of the μCAT-MPD thruster is an important parameter that impacts the physical processes. Here, we demonstrate that on the two-stage μCAT-MPD thruster, an optimal distance exists at which the thruster produces a high milli-newton thrust at high TPR and efficiency. Higher distance leads to an increased threshold voltage required for the onset of the second stage, which deteriorates the thruster’s performance, while the zero distance between the stages (in this case the MPD electrode becomes the part of the anode of the first stage) allows achieving only the moderate improvement of thrust level without any possibility to throttle it.

The work is concerned with the efficiency of inclusion of the additional layer of por-Si applied as a buffer into the growth technology of AlxGa1-xN/AlN/Si as well as its influence on the morphological parameters and composition of surface of the grown heterostructures. In the course of the study, it was found that the heterostructure grown using a nanoporous por-Si buffer layer on a Si(111) n-type monocrystalline silicon wafer has a more homogeneous structure of the epitaxial layer and its surface morphology.

By electron-beam evaporation of a solid state dielectrics (alumina ceramics) and a magnetic material (steel-3) in fore-vacuum, thin films of several μm, possessing both dielectric and magnetic properties, were deposited on a substrate. The work shows that the microstrip resonator method can be used to assess the presence of magnetic properties in films.

Small, lightweight low-power micro-cathode arc thrusters ( µ CATs) with micronewton thrust are well suited to the altitude control of small satellites like CubeSats. For some applications (orbit raising, maneuvering) their thrust level needs to be improved. A possible approach for this could be the two-staged thruster—a micro-cathode thruster with a magnetoplasmadynamic (MPD) stage and an external magnetic field. In this article, we discuss some discharge features that such a two-stage µ CAT-MPD experiences in each configuration of the magnetic field—formed with either a permanent magnet, or a pulsed magnetic coil. We found that in both configurations of the magnetic field, the thrust can be enhanced significantly (up to factor of 10) after some threshold voltage is applied to the second stage. The pulsed magnetic coil ensures better controllability of the magnetic field; however, it causes an undesirable time delay between the plasma generation moments in both stages, which consequently results in a moderate thrust increase. The permanent magnet provides a stable thrust increase; however, it cannot be switched off, which seems to be impractical for its use in micro-satellites. In both magnetic field configurations, the emissive electromagnetic noise level was found to be low-frequency (within tens of kHz) and quite moderate in amplitude, and mechanical noise was found to be two orders of magnitude lower than the thrust generated in the normal working regime.

360 nm and 700 nm thick GaAs layers were grown by MO MOCVD growth technique directly on compliant Si (100) substrate and on supper-lattice (SL) AlGaAs buffer layer. The XRD study revealed better structural quality for the sample grown on SL / por-Si buffer. AFM study revealed a smoother sample surface with blocks of more regular rectangular shape and larger size as well. Photoluminescence spectra of the samples revealed an energy shift of PL maximum intensity for both samples. Sample grown on SL buffer also showed higher PL intensity corresponding to better crystalline perfection.

Abstract 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.

Abstract 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 3 C -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.

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.

1-μm-thick GaN layers were obtained in one growth procedure on compliant SiC/Si(111) substrates using plasma-assisted molecular beam epitaxy (PA MBE). Si(111) substrates were modified by the atoms substitution technique. Prior to the atoms substitution procedure, on the one substrate, the transition porous Si layer (por-Si) was performed. The GaN layer grown on this substrate revealed better surface morphology and structural quality, less threading dislocation density, and as a result, showed lower free carrier concentration and higher carrier mobility. Moreover, the XRD study revealed less strain level in the GaN layer grown on the por-Si layer.

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.

AbstractIntegrated heterostructures exhibiting a nanocolumnar morphology of the In_ x Ga_1 –_ x N 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 In_ x Ga_1 –_ x N 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 In_ x Ga_1 –_ x N layer. The growth of In_ x Ga_1 –_ x N 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.

This paper reports on influence of the nanoporous Si buffer layer on morphological, physical and structural properties of the InxGa1-xN layer with nanocolumnar morphology of the surface, grown by plasma assisted molecular beam epitaxy on the traditional Si(111) substrates. By means of various structural and spectroscopy methods electronic structure, morphology of the surface and optical properties of grown heterostructures was studied. We showed that usage of por-Si ad-layer helps to achieve more isotropic InGaN nanocolumns diameter distribution as well as to increase PL intensity up to 25%.

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.

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.

GaN/Si(111) heterostructures grown by plasma-assisted molecular beam epitaxy on routine Si(111) substrates and compliant por-Si/Si(111) substrates without using AlN buffer layer was studied by using various structural and spectroscopy methods of analysis. XPS study revealed that the layer is grown on the compliant substrate of por-Si being closer to the stoichiometric composition. The shift of the A1(LO) mode in the Raman spectrum confirms the lattice-matched growth type on the compliant substrate in comparison with the routine c-Si substrate. The experimentally determined value of the optical bandgap width for the epitaxial GaN layer grown on por-Si substrate exceeds that of the layer grown on single-crystalline silicon c-Si by 0.1 eV

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 suffi-ciently 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.