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A drop in the efficiency of light-emitting diodes based on InGaN/GaN QWs known as the ‘green gap’ has been studied intensively over the past dozen years. Several factors were revealed to contribute to its origin, such as random fluctuations in the indium concentration or the diffusion of point defects during the growth of QWs. The aim of this paper is to demonstrate that the Kirkendall effect can be the mechanism responsible for the thermal decomposition of InGaN/GaN MQWs structures, contributing to the green gap problem. By applying density functional theory, harmonic approximation, and harmonic transition state theory, we calculated the heights of the migration energy barriers of In and Ga atoms diffusing in I n x G a 1 − x N alloys ( x = 0 , 0.11 , 0.22 ), the vibrational frequencies of I n x G a 1 − x N alloys in the presence of migrating point defects, the temperature dependencies of the defect migration energy barriers and diffusion coefficients of Ga and In atoms migrating in I n x G a 1 − x N alloys. We demonstrated the presence of unbalanced diffusion rates of In and Ga atoms at the I n x G a 1 − x N / G a N interfaces and finally explained the experimentally observed mechanism of void formation at the I n x G a 1 − x N / G a N interfaces by means of the Kirkendall effect.

The formation and diffusion of point defects have a detrimental impact on the functionality of devices in which a high quality AlN/GaN heterointerface is required. The present paper demonstrated the heights of the migration energy barriers of native point defects throughout the AlN/GaN heterointerface, as well as the corresponding profiles of energy bands calculated by means of density functional theory. Both neutral and charged nitrogen, gallium, and aluminium vacancies were studied, as well as their complexes with a substitutional III-group element. Three diffusion mechanisms, that is, the vacancy mediated, direct interstitial, and indirect ones, in bulk AlN and GaN crystals, as well at the AlN/GaN heterointerface, were taken into account. We showed that metal vacancies migrated across the AlN/GaN interface, overcoming a lower potential barrier than that of the nitrogen vacancy. Additionally, we demonstrated the effect of the inversion of the electric field in the presence of charged point defects VGa3− and VAl3− at the AlN/GaN heterointerface, not reported so far. Our findings contributed to the issues of structure design, quality control, and improvement of the interfacial abruptness of the AlN/GaN heterostructures.

Multifunctional nanocomposites from an equimolar As4S4/Fe3O4 cut section have been successfully fabricated from coarse-grained bulky counterparts, employing two-step mechanochemical processing in a high-energy mill operational in dry- and wet-milling modes (in an aqueous solution of Poloxamer 407 acting as a surfactant). As was inferred from the X-ray diffraction analysis, these surfactant-free and surfactant-capped nanocomposites are β-As4S4-bearing nanocrystalline–amorphous substances supplemented by an iso-compositional amorphous phase (a-AsS), both principal constituents (monoclinic β-As4S4 and cubic Fe3O4) being core–shell structured and enriched after wet milling by contamination products (such as nanocrystalline–amorphous zirconia), suppressing their nanocrystalline behavior. The fluorescence and magnetic properties of these nanocomposites are intricate, being tuned by the sizes of the nanoparticles and their interfaces, dependent on storage after nanocomposite fabrication. A specific core–shell arrangement consisted of inner and outer shell interfaces around quantum-confined nm-sized β-As4S4 crystallites hosting a-AsS, and the capping agent is responsible for the blue-cyan fluorescence in as-fabricated Poloxamer capped nanocomposites peaking at ~417 nm and ~442 nm, while fluorescence quenching in one-year-aged nanocomposites is explained in terms of their destroyed core–shell architectures. The magnetic co-functionalization of these nanocomposites is defined by size-extended heterogeneous shells around homogeneous nanocrystalline Fe3O4 cores, composed by an admixture of amorphous phase (a-AsS), nanocrystalline–amorphous zirconia as products of contamination in the wet-milling mode, and surfactant.

Integration of diamond with GaN-based high-electron-mobility transistors improves thermal management, influencing the reliability, performance, and lifetime of GaN-based devices. The current GaN-on-diamond integration technology requires precise interface engineering and appropriate interfacial layers. In this respect, we performed first principles calculation on the stability of diamond–GaN interfaces in the framework of density functional theory. Initially, some stable adsorption sites of C atoms were found on the Ga- and N-terminated surfaces that enabled the creation of a flat carbon monolayer. Following this, a model of diamond–GaN heterojunction with the growth direction [111] was constructed based on carbon adsorption results on GaN0001 surfaces. Finally, we demonstrate the ways of improving the energetic stability of diamond–GaN interfaces by means of certain reconstructions induced by substitutional dopants present in the topmost GaN substrate’s layer.

This study presents the results of investigating the interaction between the CeF₃–EuF₃ system and the NaCl–KCl salt melt using spectroscopic methods. It was found that CeF₃ ions undergo no significant changes upon dissolution in the NaCl–KCl melt. In contrast, the dissolution of EuF₃, both individually and within the CeF₃–EuF₃ system, is accompanied by redox reactions leading to the formation of Eu2⁺. The diffuse reflectance spectra of both the bottom (insoluble sediment) and upper parts of the solidified salt melt in the UV range indirectly indicate photoluminescence excitation from Ce3⁺ and Eu2⁺ ions. In addition, absorption bands in the near-IR region (1900–2300 cm⁻1) confirm the retention of some Eu3⁺ ions in the salt melt. The study explored the effects of various factors—including sample composition, excitation wavelength, prior and subsequent heat treatment, and medium composition—on the excitation and emission spectra of the samples. Intense 5d-4f luminescence of Ce3⁺ and Eu2⁺ ions (at 330 and 430 nm, respectively) was observed predominantly in the upper part of the salt melts, along with much weaker 4f-4f luminescence from Eu3⁺ ions. Certain parameters were optimized to reduce the luminescence contribution from Ce3⁺ and especially Eu3⁺ ions while enhancing the luminescence of Eu2⁺ ions. Solidified salt solution-melts of the NaCl–KCl–CeF₃–EuF₃ system show promise as materials for developing solar ultraviolet radiation detectors.

This study presents a detailed analysis of point defect migration in InxGa1−xN/GaN heterostructures, focusing on two indium compositions (x = 0.125, 0.25). Using density functional theory calculations, we identify the impact of indium content and temperature on the mobility of nitrogen, gallium, and indium atoms, revealing key differences in their migration energy barriers. Furthermore, we investigate the lateral diffusion of indium and gallium atoms, as well as complexes of substitutional metal atoms with vacancies, through a vacancy-mediated mechanism in individual metal layers of InxGa1−xN/GaN. Our results show that increasing indium concentration reduces migration barriers, enhancing defect mobility, particularly for indium atoms. These findings highlight the critical role of indium sublattice in promoting lattice relaxation and defect redistribution, while also elucidating the temperature-dependent dynamics of vacancy-mediated diffusion.

This study presents a detailed analysis of point defect migration in In x Ga 1 − x N / GaN heterostructures, focusing on two indium compositions ( x = 0.125, 0.25). Using density functional theory calculations, we identify the impact of indium content and temperature on the mobility of nitrogen, gallium, and indium atoms, revealing key differences in their migration energy barriers. Furthermore, we investigate the lateral diffusion of indium and gallium atoms, as well as complexes of substitutional metal atoms with vacancies, through a vacancy-mediated mechanism in individual metal layers of In x Ga 1 − x N / GaN . Our results show that increasing indium concentration reduces migration barriers, enhancing defect mobility, particularly for indium atoms. These findings highlight the critical role of indium sublattice in promoting lattice relaxation and defect redistribution, while also elucidating the temperature-dependent dynamics of vacancy-mediated diffusion.

This study presents a detailed analysis of point defect migration in\\mathrm{In_(𝑥)Ga}{₁₋ₓ}{\\mathrm{N/GaN}{}{h}}eterostructures, focusing on two indium compositions ( x = 0.125, 0.25). Using density functional theory calculations, we identify the impact of indium content and temperature on the mobility of nitrogen, gallium, and indium atoms, revealing key differences in their migration energy barriers. Furthermore, we investigate the lateral diffusion of indium and gallium atoms, as well as complexes of substitutional metal atoms with vacancies, through a vacancy-mediated mechanism in individual metal layers of\\mathrm{In_(𝑥)Ga}{₁₋ₓ}{\\mathrm{N/GaN}{}{.}} Our results show that increasing indium concentration reduces migration barriers, enhancing defect mobility, particularly for indium atoms. These findings highlight the critical role of indium sublattice in promoting lattice relaxation and defect redistribution, while also elucidating the temperature-dependent dynamics of vacancy-mediated diffusion.

This study presents the results of investigating the interaction between the CeF₃-EuF₃ system and the NaCl-KCl salt melt using spectroscopic methods. It was found that CeF₃ ions undergo no significant changes upon dissolution in the NaCl-KCl melt. In contrast, the dissolution of EuF₃, both individually and within the CeF₃-EuF₃ system, is accompanied by redox reactions leading to the formation of Eu ⁺. The diffuse reflectance spectra of both the bottom (insoluble sediment) and upper parts of the solidified salt melt in the UV range indirectly indicate photoluminescence excitation from Ce ⁺ and Eu ⁺ ions. In addition, absorption bands in the near-IR region (1900-2300 cm⁻ ) confirm the retention of some Eu ⁺ ions in the salt melt. The study explored the effects of various factors-including sample composition, excitation wavelength, prior and subsequent heat treatment, and medium composition-on the excitation and emission spectra of the samples. Intense 5d-4f luminescence of Ce ⁺ and Eu ⁺ ions (at 330 and 430 nm, respectively) was observed predominantly in the upper part of the salt melts, along with much weaker 4f-4f luminescence from Eu ⁺ ions. Certain parameters were optimized to reduce the luminescence contribution from Ce ⁺ and especially Eu ⁺ ions while enhancing the luminescence of Eu ⁺ ions. Solidified salt solution-melts of the NaCl-KCl-CeF₃-EuF₃ system show promise as materials for developing solar ultraviolet radiation detectors.

This study presents the results of investigating the interaction between the CeF₃–EuF₃ system and the NaCl–KCl salt melt using spectroscopic methods. It was found that CeF₃ ions undergo no significant changes upon dissolution in the NaCl–KCl melt. In contrast, the dissolution of EuF₃, both individually and within the CeF₃–EuF₃ system, is accompanied by redox reactions leading to the formation of Eu[sup.2]⁺. The diffuse reflectance spectra of both the bottom (insoluble sediment) and upper parts of the solidified salt melt in the UV range indirectly indicate photoluminescence excitation from Ce[sup.3]⁺ and Eu[sup.2]⁺ ions. In addition, absorption bands in the near-IR region (1900–2300 cm⁻[sup.1]) confirm the retention of some Eu[sup.3]⁺ ions in the salt melt. The study explored the effects of various factors—including sample composition, excitation wavelength, prior and subsequent heat treatment, and medium composition—on the excitation and emission spectra of the samples. Intense 5d-4f luminescence of Ce[sup.3]⁺ and Eu[sup.2]⁺ ions (at 330 and 430 nm, respectively) was observed predominantly in the upper part of the salt melts, along with much weaker 4f-4f luminescence from Eu[sup.3]⁺ ions. Certain parameters were optimized to reduce the luminescence contribution from Ce[sup.3]⁺ and especially Eu[sup.3]⁺ ions while enhancing the luminescence of Eu[sup.2]⁺ ions. Solidified salt solution-melts of the NaCl–KCl–CeF₃–EuF₃ system show promise as materials for developing solar ultraviolet radiation detectors.