Energy crisis and environmental pollution require efficient photocatalysts for hydrogen production through hydrolysis and good photoabsorbers for solar energy conversion. Therefore, we designed a SiS2/SiSe2 van der Waals heterojunction (vdWH) monolayer as a photocatalyst and photoabsorber. Based on first-principles calculations combined with semi-empirical maximally localized Wannier function tight-binding (MLWF-TB) method, it is revealed that SiS2/SiSe2 vdWH is a semiconductor with an indirect band gap characterized by staggered band alignment, which facilitates the separation of electrons and holes , inhibiting electron-hole recombination. Additionally, the excitonic effects play a significant role in describing the linear optical response in these systems, resulting in an exciton binding energy closer to 300 meV and a small optical anisotropy surge. The solar harvesting analysis shows a solar harvesting efficiency closer to 20 % in the vdWH, showcasing performance enhancement when compared with the isolated monolayers. Our theoretical findings shed light on the design of novel nonmetal-based photocatalysts for water splitting and provide useful guidelines for future experiments.

We considered the problem of localization of electrons and holes taking for instance the pyramidal InAs quantum dots in GaAs. The problem of quantum mechanics was solved for the localizing potential taking into account the geometry, chemical composition and built-in fields of the mechanical stress and strain. We found that the strongest localization of both types of charge carriers can be achieved if the ratio of the pyramid height to its base is about 0.2. Keywords: quantum dots, elastic strain, charge carrier localization.

We perform numerical modeling of the optical absorption spectra of metamaterials composed of systems of semimetal antimony nanoparticles embedded into AlxGa1−xAs semiconductor matrices. We reveal a localized surface plasmon resonance (LSPR) in these metamaterials, which results in a strong optical extinction band below, near, or above the direct band gap of the semiconductor matrices, depending on the chemical composition of the solid solutions. We elucidate the role of dielectric losses in AlxGa1−xAs, which impact the LSPR and cause non-plasmonic optical absorption. It appears that even a dilute system of plasmonic Sb nanoinclusions can substantially change the optical absorption spectra of the medium.

We study the formation of a superradiant optical mode in the room temperature reflection spectra from resonant Bragg structures (RBSs) composed of single and double (In,Ga)N quantum wells (QWs) in the unit cell. The appearance of the mode manifests itself by a significant increase in the resonant optical reflectivity due to the electromagnetic coupling of quasi-two-dimensional excitons in the QWs. The implementation of the supercells with double (In,Ga)N QWs results in an increase in the oscillator strength of the quasi-2D excitons and corresponding rise of the radiative broadening parameter to the value as high as 0.3 +/- 0.02 meV. We also show that the supercells with double QWs are preferable for RBS with large number of periods due to better tolerance to deviations from the exact periodicity.

Initial stage of precipitate formation during post-growth annealing of nonstoichiometric GaAs and GaAs0.97Sb0.03 grown by low-temperature (150°C) MBE on GaAs (001) substrate with intermediate growth interruption and simultaneous heating up to 250°C was studied by transmission electron microscopy. Short-term intermediate heating despite the low temperature was revealed to result in the precipitation of larger particles during subsequent post-growth annealing compared to the material not subjected to such heating. This effect is explained by the huge concentration of excess arsenic in LT-GaAs and LT-GaAs0.97Sb0.03 grown at 150°C, enhanced diffusion due to the high concentration of nonequilibrium gallium vacancies, and non-threshold nucleation.

We reveal the feasibility of the localized surface plasmon resonance in a system of Bi nanoparticles embedded into an AlxGa1−xAs semiconductor matrix. With an ab initio determined dielectric function for bismuth and well-known dielectric properties of AlxGa1−xAs solid solution, we performed calculations of the optical extinction spectra for such metamaterial using Mie’s theory. The calculations demonstrate a strong band of the optical extinction using the localized surface plasmons near a photon energy of 2.5 eV. For the semiconducting matrices with a high aluminum content x>0.7, the extinction by plasmonic nanoparticles plays the dominant role in the optical properties of the medium near the resonance photon energy.

by molecular-beam epitaxy we have grown epitaxial layers of GaAs1–xBix solid solutions with a bismuth content of 0 < x < 0.02. Structural and optical properties of the layers were investigated. We determine the influence of the bismuth flux and substrate temperature on the bismuth incorporation into the growing layers.

We experimentally demonstrate the formation of a superradiant optical mode in the room-temperature reflection spectra from a resonant Bragg structure composed of 30 equidistant GaN quantum wells separated by (Al,Ga)N barriers. The mode arises when the condition of the Bragg diffraction is fulfilled at the wavelength corresponding to the energy of the quasi-two-dimensional excitons in the quantum wells. It manifests itself as a significant increase in the amplitude and a change in the shape of the resonant optical reflection due to the electromagnetic coupling of the excitons. By modeling of the optical spectra, we evaluate the radiative and non-radiative broadening parameters of the excitonic states in the GaN quantum wells, which appear to be 0.4 +/- 0.02 and 40 +/- 5 meV, correspondingly, for the resonant exciton energy of 3.605 eV. The resonant Bragg structure based on the periodic sequence of the GaN quantum wells demonstrates an efficient coupling of photons and excitons at room temperature, which makes it promising for device applications.

Room-temperature reflectance spectra are recorded for a resonant Bragg structure with 30 GaN/AlGaN quantum wells. Accurate quantitative fitting of the experimental results is achieve by means of transfer matrix numerical modeling. Parameters of radiative and nonradiative exciton broadening in the GaN/AlGaN quantum wells are determined.

Epitaxial layers of Al x Ga 1-x As 1-y Sb y with an aluminum content x~60% and antimony content y~3% were successfully grown by molecular-beam epitaxy at low temperature. A developed system of AsSb nanoinclusions was formed in the semiconductor matrix by subsequent annealing. The extended transparency window of the obtained metamaterial allows us to document the absorption of light near the interband absorption edge of the Al x Ga 1-x As 1-y Sb y semiconductor matrix. Parameters of the observed extinction band allow us to attribute the optical absorption to the plasmon resonance in the system of AsSb nanoinclusions. Keywords: molecular beam epitaxy, x-ray diffraction analysis, transmission electron microscopy, optical properties, plasmon resonance.

We studied an effect of spatial disorder on the optical response of resonant Bragg structures with InGaN quantum wells. Using an experimentally verified model, we calculated a transformation of the optical reflection from the resonant Bragg structures with 60, 100, and 200 quantum wells as a function of the degree of disorder in the system. A critical threshold deviation from the exact periodicity was revealed, which causes a qualitative change of the optical resonance.

Методом молекулярно-лучевой эпитаксии при низкой температуре с использованием прерываний роста успешно выращены эпитаксиальные слои Al x Ga 1-x As 1-y Sb y с содержанием алюминия x~60% и содержанием сурьмы y~3%. Путем последующего отжига в полупроводниковой матрице сформирована развитая система нановключений AsSb. Увеличенное окно прозрачности полученного метаматериала позволило надежно документировать широкую полосу поглощения света вблизи края межзонного поглощения полупроводниковой матрицы Al x Ga 1-x As 1-y Sb y . Параметры наблюдаемой полосы экстинкции позволяют связать такое поглощение света с плазмонным резонансом в системе нановключений AsSb. Ключевые слова: молекулярно-лучевая эпитаксия, рентгенодифракционный анализ, просвечивающая электронная микроскопия, оптические свойства, плазмонный резонанс.

Reflection spectra from a resonant Bragg structure with 30 GaN/AlGaN quantum wells have been measured at room temperature. Numerical modeling using the method of transfer matrices gave a quantitatively accurate fit of the experimental results. Defined radiative and non-radiative broadening parameters of the exciton in GaN/AlGaN quantum wells.

We analyze the possibility to realize a localized surface plasmon resonance in metamaterials composed of As1−zSbz nanoparticles embedded in an AlxGa1−xAs1−ySby semiconductor matrix. To this end, we perform ab initio calculations of the dielectric function of the As1−zSbz materials. Changing the chemical composition z, we trace the evolution of the band structure, dielectric function, and loss function. In terms of the Mie theory, we calculate the polarizability and optical extinction of a system of As1−zSbz nanoparticles in an AlxGa1−xAs1−ySby environment. We show a possibility to provide localized surface plasmon resonance near the band gap of the AlxGa1−xAs1−ySby semiconductor matrix by a built-in system of As1−zSbz nanoparticles strongly enriched by Sb. The results of our calculations are supported by available experimental data.

AlGaAsSb and AlGaAs films as thick as 1 μm with Al content as high as 60% were successfully grown by low-temperature (200 °C) MBE. To overcome the well-known problem of growth disruption due to a high aluminum content and a low growth temperature, we applied intermittent growth with the temperature elevation to smooth out the emerging roughness of the growth front. Post-growth annealing of the obtained material allowed us to form a developed system of As or AsSb nanoinclusions, which occupy 0.3–0.6% of the material volume. While the As nanoinclusions are optically inactive, the AsSb nanoinclusions provide a strong optical absorption near the band edge of the semiconductor matrix due to the Fröhlich plasmon resonance. Owing to the wider bandgap of the grown Al0.6Ga0.4As0.97Sb0.03 compound, we have expanded the spectral range available for studying the Fröhlich plasmon resonance. The grown metamaterial represents an optically active medium of which the formation process is completely compatible with the epitaxial growth technology of semiconductors.

The optical properties of a structure with a periodic system of 100 InGaN quantum wells separated by nontunneling GaN barriers are investigated at room temperature. The structure periodicity corresponds to the Bragg-diffraction condition at the quantum-well exciton frequency. The results of numerical simulation using transfer matrices are in reasonable quantitative agreement with the experimental data. The model includes the resonance response of A, B, and C excitons in the quantum wells and the optical absorption tail in the barrier and buffer layers. The radiative and nonradiative damping rates of excitons in the InGaN quantum wells are determined.

by molecular-beam epitaxy we have grown epitaxial layers of GaAs 1– x Bi x solid solutions with a bismuth content of 0 < x < 0 . 02. Structural and optical properties of the layers were investigated. We determine the influence of the bismuth flux and substrate temperature on the bismuth incorporation into the growing layers.

We develop a model of an epitaxial self-organized InGaAs quantum dot buried in GaAs, which takes into account experimentally determined indium distribution inside the QD, its geometry and crystallography. The problem of solid mechanics was solved to determine the stress-strain field. Then, the parameters of the electron and hole ground states were evaluated by solving the problem of the quantum mechanics on the same mesh. The results of calculations appeared to be reasonably well consistent with experimentally recorded optical emission spectra for the QDs in the same sample. The experimentally-verified modeling reveals a bagel-like shape of the hole wave function at the ground state, which should considerably impact the optical and magnetic properties of the QDs. Such shape of the wave function is beyond the predictions of simplified models with uniform indium distribution.

By molecular-beam epitaxy we have grown epitaxial layers of GaAs1-xBix solid solutions with a bismuth content of 0 < x < 0.02. Structural and optical properties of the layers were investigated. We determine the influence of the bismuth flux and substrate temperature on the bismuth incorporation into the growing layers.

We show that a self-organized quantum dot (QD) embedded in a quantum well (QW) can provide better carrier localization compared to the bare QD due to a complex action of three processes, namely, an increase in the QD volume, a change of the QD aspect ratio, and strain redistribution provided by the QW. For an InAs QD and an (In,Ga)As QW, we calculate the possible energy benefits of these three contributions and examine the optimal dot-in-well configuration sustaining the interface coherency.