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Мигас, Дмитрий Борисович

Организационные подразделения

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Институт нанотехнологий в электронике, спинтронике и фотонике

Институт ИНТЭЛ занимается научной деятельностью и подготовкой специалистов в области исследования физических принципов, проектирования и разработки технологий создания компонентной базы электроники гражданского и специального назначения, а также построения современных приборов на её основе. Наша основная цель – это создание и развитие научно-образовательного центра мирового уровня в области наноструктурных материалов и устройств электроники, спинтроники, фотоники, а также создание эффективной инновационной среды в области СВЧ-электронной и радиационно-стойкой компонентной базы, источников ТГц излучения, ионно-кластерных технологий материалов.

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Мигас

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Дмитрий Борисович

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Теперь показываю 1 - 10 из 27

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Marked enhancement of the photoresponsivity and minority-carrier lifetime of BaS i2 passivated with atomic hydrogen
(2019) Xu, Z.; Shohonov, D. A.; Filonov, A. B.; Gotoh, K.; Migas, D. B.; Borisenko, V. E.; Мигас, Дмитрий Борисович
© 2019 American Physical Society.Passivation of barium disilicide (BaSi2) films is very important for their use in solar cell applications. In this paper, we demonstrated the effect of hydrogen (H) passivation on both the photoresponsivity and minority-carrier lifetime of BaSi2 epitaxial films grown by molecular beam epitaxy. First, we examined the growth conditions of a 3-nm-thick hydrogenated amorphous silicon (a-Si) capping layer formed on a 500-nm-thick BaSi2 film and found that an H supply duration (ta-Si:H) of 15 min at a substrate temperature of 180 °C sizably enhanced the photoresponsivity of the BaSi2 film. We next supplied atomic H to BaSi2 epitaxial films at 580 °C and changed supply duration (tBaSi;H) in the range of 1-30 min, followed by capping with an a-Si layer. The photoresponsivity of the films changed considerably depending on tBaSi;H and reached a maximum of 2.5 A/W at a wavelength of 800 nm for the sample passivated for tBaSi;H=15 min under a bias voltage of 0.3 V applied to the front-surface indium-tin-oxide electrode with respect to the back-surface aluminum electrode. This photoresponsivity is approximately one order of magnitude higher than the highest value previously reported for BaSi2. Microwave photoconductivity decay measurements revealed that the minority-carrier lifetime of the BaSi2 film with the highest photoresponsivity was 14 μs, equivalent to its bulk carrier lifetime ever reported. We performed theoretical analyses based on a rate equation including several recombination mechanisms and reproduced the experimentally obtained decay curves. We also calculated the total density of states of BaSi2 by ab initio studies when one Si vacancy existed in a unit cell and one, two, and three H atoms occupied Si vacancy or interstitial sites. A Si vacancy caused a localized state with two energy bands to appear close to the middle of the band gap. In certain cases, H passivation of the Si dangling bonds can markedly decrease trap concentration. From both experimental and theoretical viewpoints, we conclude that an atomic H supply is beneficial for BaSi2 solar cells.
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Thermodynamic driving force in the formation of hexagonal-diamond Si and Ge nanowires
(2021) Scalise, E.; Sarikov, A.; Barbisan, L.; Marzegalli, A.; Migas, D. B.; Мигас, Дмитрий Борисович
© 2021 Elsevier B.V.The metastable hexagonal-diamond phase of Si and Ge (and of SiGe alloys) displays superior optical properties with respect to the cubic-diamond one. Based on first-principle calculations we show that the surface energy of the typical facets exposed in Si and Ge nanowires is lower in the hexagonal-diamond phase than in the cubic one. By exploiting a synergic approach based also on a recent state-of-the-art interatomic potential and on a simple geometrical model, we investigate the relative stability of nanowires in the two phases up to few tens of nm in radius, highlighting the surface-related driving force and discussing its relevance in recent experiments. We also explore the stability of Si and Ge core-shell nanowires with hexagonal cores (made of GaP for Si nanowires, of GaAs for Ge nanowires). In this case, the stability of the hexagonal shell over the cubic one is also favored by the energy cost associated with the interface linking the two phases. Interestingly, our calculations indicate a critical radius of the hexagonal shell much lower than the one reported in recent experiments, indicating the presence of a large kinetic barrier allowing for the enlargement of the wire in a metastable phase.
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Mechanisms of carrier lifetime enhancement and conductivity-type switching on hydrogen-incorporated arsenic-doped BaSi2
(2021) Aonuki, S.; Xu, Z.; Yamashita, Y.; Gotoh, K.; Migas, D. B.; Мигас, Дмитрий Борисович
© 2021 Elsevier B.V.A comparative experimental and theoretical study of the role of H incorporation in As-doped BaSi2 films has been carried out based on the experimental results that an optimal time of H treatment for the increase in photoresponsivity and carrier lifetime was in the range of 1 – 20 min. Adequate theoretical representation of the decay curves in the framework of the model for non-radiative processes accounted for various trap-related recombination mechanisms to estimate the trap concentration to be in the range of 1.9 × 1013 to 1.7 × 1014 cm−3. Additionally, the extended theoretical ab initio quantum-chemical simulation of the electronic structure of the studied systems was performed. It was revealed that interstitial As atoms can mostly provide trap states in the gap while H atoms neutralize such traps. The experimentally observed unexpected switching in conductivity from n-type to p-type and vice versa in As-doped BaSi2 with H incorporation was explained to specific configurations of point defects (an As impurity with a H atom in different positions and various interatomic As-H distances) which affect the position of states in the gap.
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Stability of 2D Alkaline-Earth Metal Silicides, Germanides and Stannides
(2019) Alekseev, A. Yu.; Chernykh, A. G.; Filonov, A. B.; Skorodumova, N. V.; Migas, D. B.; Мигас, Дмитрий Борисович
By means of ab initio calculations, we have estimated stability of 2D Me2X (Me = Mg, Ca, Sr, Ba and X = Si, Ge, Sn) in the T and Td phases, which are similar to the ones of 2D transition metal chalcogenides, in addition to their phonon spectra. The T phase is found to be more stable for 2D Ca2X, Sr2X and Ba2X, whereas the Td phase is predicted to be the ground state for 2D Mg2X. We have also discussed that imaginary frequencies in the calculated phonon spectra of 2D Me2X, which appeared in the vicinity of the Gamma point, were not necessarily associated with the dynamic instability.
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Curvature-induced effects in semiconducting alkaline-earth metal silicide nanotubes
(2021) Alekseev, A. Y.; Filonov, A. B.; Chernykh, A. G.; Skorodumova, N. V.; Migas, D. B.; Borisenko, V. E.; Мигас, Дмитрий Борисович
© 2020 Elsevier B.V.By means of ab-initio techniques we have investigated changes in the structure and electronic properties of alkaline-earth metal silicide (Ca2Si, Mg2Si and MgCaSi) nanotubes caused by the curvature-induced effects. It is revealed that the curvature-induced effects can: 1) stabilize Mg2Si nanotubes in a phase, which is metastable for the parent 2D Mg2Si; 2) lead to an energy gain as a result of 2D to nanotube structural transformation in the case of ternary MgCaSi nanotubes; 3) modify the band dispersion and band gaps for nanotubes with the diameters less than 30 Å. In addition, Mg2Si and MgCaSi nanotubes are found to be direct band-gap (0.5–1.2 eV) materials with appreciable oscillator strength of the first direct transitions.
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New monoclinic ground state of FeSi
(2024) Galkin, N. G.; Migas, D. B.; Medvedeva, N. V.; Filonov, A. B.; Мигас, Дмитрий Борисович
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Interplay between structural changes, surface states and quantum confinement effects in semiconducting Mg2Si and Ca2Si thin films
(2023) Alekseev, A. Y.; Migas, D. B.; Filonov, A. B.; Galkin, N. G.; Мигас, Дмитрий Борисович
Ab initio techniques have been used to investigate structural changes in semiconducting Mg2Si and Ca2Si thin films (from 17 nm down to 0.2 nm corresponding to the 2D structure) along with band-gap variations due to quantum confinement. Cubic Mg2Si(111) thin films being dynamically stable at thicknesses (d) larger than 0.3 nm displayed an indirect band gap, the reduction of which with increasing d could be reasonably well described by the simple effective mass approximation. Only 2D Mg2Si has a unique structure because of the orthorhombic distortion and the direct band gap. Since the surface energy of cubic Ca2Si(111) films was lower with respect to any surface of the orthorhombic phase, which is the ground state for the Ca2Si bulk, the metastable in-bulk cubic phase in the form of thin films turned out to be preferable in total energy than any orthorhombic Ca2Si thin film for d < 3 nm. Sizable structural distortion and the appearance of surface states in the gap region of Ca2Si thin films with d < 3 nm could be the reason for an odd dependence of the band-gap variation on d.
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Theoretical analysis of electrochromism of Ni-deficient nickel oxide - from bulk to surfaces
(2023) Pasti, I. A.; Dobrota, A. S.; Migas, D. B.; Johansson, B.; Мигас, Дмитрий Борисович
The development of new electrochromic materials and devices, like smart windows, has an enormous impact on the energy efficiency of modern society. One of the crucial materials in this technology is nickel oxide. Ni-deficient NiO shows anodic electrochromism, whose mechanism is still under debate. We use DFT+U calculations to show that Ni vacancy generation results in the formation of hole polarons localized at the two oxygens next to the vacancy. In the case of NiO bulk, upon Li insertion or injection of an extra electron into Ni-deficient NiO, one hole gets filled, and the hole bipolaron is converted into a hole polaron well-localized at one O atom, resulting from the transition between oxidized (colored) to reduced (bleached) state. In the case of the Ni-deficient NiO(001) surface, the qualitatively same picture is obtained upon embedding Li, Na, and K into the Ni surface vacancy, reinforcing the conclusion that the electron injection, resulting in the filling of the hole states, is responsible for the modulation of the optical properties of NiO. Hence, our results suggest a new mechanism of Ni-deficient NiO electrochromism not related to the change of the Ni oxidation states, i.e., the Ni2+/Ni3+ transition, but based on the formation and annihilation of hole polarons in oxygen p-states.
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Temperature induced structural and polarization features in BaFe12O19
(2023) Migas, D. B.; Turchenko, V. A.; Rutkauskas, A. V.; Trukhanov, S. V.; Мигас, Дмитрий Борисович
We report the observation of a peculiar polarization behavior of BaFe 12 O 19 in electric field where the linear polarization is detected at temperatures below 150 K whereas at higher temperatures a hysteresis-like polarization response is observed.
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Crystal Structure, Optical Properties, and Characteristics of the Band Gap of Ca2Si Semiconductor Films on an Al2O3(0001) Substrate
(2022) Galkin, N. G.; Galkin, K. N.; Chernev, I. M.; Kropachev, O. V.; Goroshko, D. L.; Subbotin, E. Y.; Migas, D. B.; Мигас, Дмитрий Борисович