Plasma Activation Of Nitrogen Research Articles

Carrier Scattering Analysis in AlN/GaN HEMT Heterostructures with an Ultrathin AlN Barrier

Experimental AlN/GaN heterostructures (HSs) with an ultrathin AlN barrier were obtained using molecular beam epitaxy with plasma activation of nitrogen. The layer resistance of the optimized structures was less than 230 Ω/¨. The scattering processes that limit the mobility of two-dimensional electron gas in undoped AlN/GaN HSs with an ultrathin AlN barrier have been studied. It is shown that in the ns range characteristic of AlN/GaN HEMT HSs (ns 1 × 1013 cm–2), a noticeable contribution to the scattering of charge carriers is made by the roughness of the heterointerface.

Coordinated d-p hybridized hcp@fcc NiRu alloy doped by interstitial atoms for boosting urea-assisted simulated seawater electrolysis at industrial current densities

The production of hydrogen through seawater electrolysis has recently garnered increasing concern. However, hydrogen evolution reaction (HER) by alkaline seawater electrocatalysis is severely impeded by the slow H2O adsorption and H* binding kinetics at industrial current densities. Herein, a face-centered cubic/hexagonal close packed (fcc/hcp) NiRu alloy heterojunction was fabricated on Ni foam (N doped NiRu-inf/NF) by a low-temperature nitrogen plasma activation. Simultaneously, nitrogen atoms are introduced into the alloy to facilitate d-p hybridization. When N doped NiRu-inf/NF is integrated into a dual-electrode cell for urea-assisted seawater electrolysis, it achieves 100 mA cm−2 with an ultra-low voltage of 1.36 V and excellent stability. Density functional theory (DFT) verifies that the robust d-p hybridization among Ni, Ru and N exhibits more energy level matching for H2O molecule adsorption at the Ru sites, while simultaneously reducing the interaction between H* and Ni sites in N-doped NiRu-inf.

Relationship Between the Rate of Photochemical Metal-Assisted Etching of GaN Layers and Multifractal Parameters of Their Surface Structure

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.

Формирование методом молекулярно-пучковой эпитаксии с плазменной активацией азота гетероструктур с множественными квантовыми ямами InN/InGaN на сапфире

The features of the process of growth of multilayer heterostructures with InN/InGaN quantum wells (QWs) by the method of molecular-beam epitaxy with nitrogen plasma activation in the mode of modulated metal fluxes are studied. To compensate for elastic stresses in the structure, the active region was formed in the form of an InN/InGaN superlattice matched over the average lattice parameter with the underlying InGaN buffer layer. It has been shown that during the growth of relatively narrow InN QWs up to 3 nm wide, there is no relaxation of elastic stresses in the active region of the structure, and the dislocation density remains at the level ND ∼ (3−4) · 10^10 cm−2, which corresponds to the dislocation density in InGaN buffer. Such structures demonstrate the most intense PL in the wavelength range of 1.3−1.5 µm. With the growth of wider QWs, the imperfection of the structures sharply increases (ND > 10^11 cm−2), which is accompanied by a decrease in the emission intensity. The structures grown with InN/InGaN QWs demonstrated an order of magnitude better temperature stability of PL compared to bulk InN layers (PL quenching by ∼ 3 and ∼ 25 times, respectively, in the temperature range of 77−300 K). Nevertheless, at a low temperature (T = 77 K), the PL intensity of the studied structures with InN/InGaN QWs is noticeably inferior to that for the bulk InN layer, which apparently indicates a significant role of nonradiative recombination by the Shockley−Reed−Hall mechanism in structures with QWs (as opposed to Auger recombination in bulk InN).

Formation of heterostructures with multiple quantum wells InN/InGaN by the PA-MBE method on sapphire

The features of the process of growth of multilayer heterostructures with InN/InGaN quantum wells (QWs) by the method of molecular-beam epitaxy with nitrogen plasma activation in the mode of modulated metal fluxes are studied. To compensate for elastic stresses in the structure, the active region was formed in the form of an InN/InGaN superlattice matched over the average lattice parameter with the underlying InGaN buffer layer. It has been shown that during the growth of relatively narrow InN QWs up to 3 nm wide, there is no relaxation of elastic stresses in the active region of the structure, and the dislocation density remains at the level N_D~(3-4)·1010 cm-2, which corresponds to the dislocation density in InGaN-buffer. Such structures demonstrate the most intense PL in the wavelength range of 1.3-1.5 μm. With the growth of wider QWs, the imperfection of the structures sharply increases (N_D>1011 cm-2), which is accompanied by a decrease in the emission intensity. The structures grown with InN/InGaN QWs demonstrated an order of magnitude better temperature stability of PL compared to bulk InN layers (PL quenching by ~3 and ~25 times, respectively, in the temperature range of 77-300 K). Nevertheless, at a low temperature (T=77 K), the PL intensity of the studied structures with InN/InGaN QWs is noticeably inferior to that for the bulk InN layer, which apparently indicates a significant role of nonradiative recombination by the Shockley--Reed--Hall mechanism in structures with QWs (as opposed to Auger recombination in bulk InN). Keywords: indium and gallium nitride, molecular beam epitaxy, quantum well, photoluminescence, dislocations.

Формирование слоев InGaN средних составов методом МПЭ ПА для лазерных источников красного и ИК диапазона

This paper presents the results of studying the growth of InGaN layers with a high (50-80%) indium content by molecular beam epitaxy with nitrogen plasma activation on sapphire substrates with GaN/AlN buffer layers. It is shown that the processes of dissociation and phase separation of the growing InGaN layer, which occur in structures with an indium fraction of about 50%, cannot be suppressed due to the transition to a lower temperature growth (470°C - 390°C) without significant degradation of the crystalline quality of the formed structures and a sharp decrease in their emissivity. As an alternative approach to suppressing diffusion processes on the growth surface and, as a result, obtaining homogeneous InGaN layers with an [In] content of ~ 50%, high-temperature (470°C) growth under highly nitrogen-enriched conditions (flux ratio III/V ~ 0.6) was tested. The InGaN layers grown in this way show intense photoluminescence, while at the same time showing no signs of phase separation according to X-ray diffraction data. This is critically important for the possibility of implementing optical amplification and laser generation in such structures in the red region of the spectrum and in the immediately adjacent part of the near infrared region.

PA MBE growth of intermediate-composition InGaN layers for red and near-IR laser sources

This paper presents the results of studying the growth of InGaN layers with a high (50-80%) indium content by molecular beam epitaxy with nitrogen plasma activation on sapphire substrates with GaN/AlN buffer layers. It is shown that the processes of dissociation and phase separation of the growing InGaN layer, which occur in structures with an indium fraction of about 50%, cannot be suppressed due to the transition to a lower temperature growth (470oC->390oC) without significant degradation of the crystalline quality of the formed structures and a sharp decrease in their emissivity. As an alternative approach to suppressing diffusion processes on the growth surface and, as a result, obtaining homogeneous InGaN layers with an [In] content ~50%, high-temperature (470oC) growth under highly nitrogen-enriched conditions (flux ratio III/V ~0.6) was tested. The InGaN layers grown in this way show intense photoluminescence, while at the same time showing no signs of phase separation according to X-ray diffraction data. This is critically important for the possibility of implementing optical amplification and laser generation in such structures in the red region of the spectrum and in the immediately adjacent part of the near infrared region. Keywords: indium and gallium nitride, molecular beam epitaxy, spinodal decomposition, photoluminescence.

Рост тонкопленочных AlGaN/GaN эпитаксиальных гетероструктур на гибридных подложках, содержащих слои карбида кремния и пористого кремния

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.

Особенности структурных и оптических свойств InGaN-слоев, полученных методом МПЭ ПА с импульсной подачей потоков металлов

This paper presents the results of studying the properties of InGaN layers with a high InN content (80-90%) obtained by molecular beam epitaxy with plasma activation of nitrogen on sapphire substrates with AlN / GaN buffer layers. The InGaN layers were formed using the metal modulated epitaxy (MME) method, as well as in nitrogen and metal rich conditions. It was found that the use of the MME method leads to a decrease in the density of threading dislocations in the InGaN layers. Nevertheless, despite the higher dislocation density, the smallest threshold of stimulated emission of ~ 20 kW / cm2 at 77 K was obtained for the In0.8Ga0.2N layer grown under nitrogen rich conditions, which is associated with the lowest background electron concentration in this sample (1.6•1019 cm-3).

Influence of a Nanoporous Silicon Layer on the Practical Implementation and Specific Features of the Epitaxial Growth of GaN Layers on SiC/por-Si/c-Si Templates

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.

HRXRD study of the effect of a nanoporous silicon layer on the epitaxial growth quality of GaN layer on the templates of SiC/por-Si/c-Si

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.

Влияние слоя нанопористого кремния на практическую реализацию и особенности эпитаксиального роста слоев GaN на темплейтах SiC/por-Si/c-Si

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.

Photoemission Studies of the Electronic Structure of GaN Grown by Plasma Assisted Molecular Beam Epitaxy

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.

Metal-Assisted Photochemical Etching of N- and Ga-Polar GaN Epitaxial Layers

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.

Emission Properties of Heavily Doped Epitaxial Indium-Nitride Layers

The results of studies of the spontaneous photoluminescence and stimulated emission spectra of epitaxial n-InN layers with a concentration of free electrons of ~1019 cm–3 are reported. The layers are grown by molecular-beam epitaxy with the plasma activation of nitrogen on sapphire substrates with AlN and GaN buffer layers. It is found that, as the InN layers are grown under conditions with enrichment with nitrogen at a growth temperature elevated to 470°C close to the beginning of the decomposition of InN, the crystal quality of the layers is improved and the stimulated-emission threshold is lowered. As the conditions of growth change to conditions with enrichment with the metal, two emission bands separated by an energy of 100 meV are observed in the spontaneous-photoluminescence spectra of InN. For such layers, a substantial increase in the stimulated-emission threshold and, in some cases, the lack of a transition to stimulated emission are observed. In the study, an interpretation of the observed emission bands is given and some inferences as to their nature are made.

Influence of a por-Si Buffer Layer on the Optical Properties of Epitaxial InxGa1 –xN/Si(111) Heterostructures with a Nanocolumnar Film Morphology

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.

Излучательные свойства сильно легированных эпитаксиальных слоев нитрида индия

AbstractThe results of studies of the spontaneous photoluminescence and stimulated emission spectra of epitaxial n -InN layers with a concentration of free electrons of ~10^19 cm^–3 are reported. The layers are grown by molecular-beam epitaxy with the plasma activation of nitrogen on sapphire substrates with AlN and GaN buffer layers. It is found that, as the InN layers are grown under conditions with enrichment with nitrogen at a growth temperature elevated to 470°C close to the beginning of the decomposition of InN, the crystal quality of the layers is improved and the stimulated-emission threshold is lowered. As the conditions of growth change to conditions with enrichment with the metal, two emission bands separated by an energy of 100 meV are observed in the spontaneous-photoluminescence spectra of InN. For such layers, a substantial increase in the stimulated-emission threshold and, in some cases, the lack of a transition to stimulated emission are observed. In the study, an interpretation of the observed emission bands is given and some inferences as to their nature are made.

Влияние буферного слоя por-Si на оптические свойства эпитаксиальных гетероструктур In-=SUB=-x-=/SUB=-Ga-=SUB=-1-x-=/SUB=-N/Si(111) с наноколончатой морфологией пленки

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.

Металл-усиленное фотохимическое травление N- и Ga-полярных эпитаксиальных слоев GaN

The results of the study of photochemical etching without the application of external voltage, structures with Ga- and N-polar GaN layers synthesized by molecular beam epitaxy with plasma activation of nitrogen are presented. It is shown that the etching rate of layers with different polarities is very different. In this case, the use of gold-based masks for etching of GaN layers instead of titanium also makes it possible to increase the etching rate of the layers.

Effect of a por-Si Buffer Layer on the Structure and Morphology of Epitaxial InxGa1 – xN/Si(111) Heterostructures

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%).