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Peter V Sushko - One of the best experts on this subject based on the ideXlab platform.
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Band Gap Reduction and dopant interaction in epitaxial la cr co doped srtio3 thin films
Chemistry of Materials, 2014Co-Authors: Ryan B Comes, Peter V Sushko, Steve M Heald, Robert J Colby, Mark E Bowden, Scott A ChambersAbstract:We show that by co-doping SrTiO3 (STO) epitaxial thin films with equal amounts of La and Cr, it is possible to produce films with an optical Band Gap ∼0.9 eV lower than that of undoped STO. Sr1–xLaxTi1–xCrxO3 thin films were deposited by molecular beam epitaxy and characterized using X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy to show that the Cr dopants are almost exclusively in the Cr3+ oxidation state. Extended X-ray absorption fine structure measurements and theoretical modeling suggest that it is thermodynamically preferred for La and Cr dopants to occupy nearest-neighbor A- and B-sites in the lattice. Transport measurements show that the material exhibits variable-range hopping conductivity with high resistivity. These results create new opportunities for the use of doped STO films in photovoltaic and photocatalytic applications.
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optical absorption and Band Gap Reduction in fe1 xcrx 2o3 solid solutions a first principles study
Journal of Physical Chemistry C, 2013Co-Authors: Yong Wang, Kenneth Lopata, Scott A Chambers, Niranjan Govind, Peter V SushkoAbstract:We provide a detailed theoretical analysis of the character of optical transitions and Band Gap Reduction in (Fe1–xCrx)2O3 solid solutions using extensive periodic model and embedded cluster calculations. Time-dependent density functional theory is used to calculate and assign optical absorption Bands for x = 0.0, 0.5, and 1.0 and photon energies up to 5 eV. Consistent with recent experimental data, a Band Gap Reduction of as much as 0.7 eV with respect to that of pure α-Fe2O3 is found. This result is attributed predominantly to two effects: (i) the higher valence Band edge for x ≈ 0.5, as compared to those in pure α-Fe2O3 and α-Cr2O3, and (ii) the onset of Cr → Fe d–d excitations in the solid solutions. Broadening of the valence Band due to hybridization of O 2p with Fe and Cr 3d states also contributes to Band Gap Reduction.
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Optical Absorption and Band Gap Reduction in (Fe1–xCrx)2O3 Solid Solutions: A First-Principles Study
Journal of Physical Chemistry C, 2013Co-Authors: Yong Wang, Kenneth Lopata, Scott A Chambers, Niranjan Govind, Peter V SushkoAbstract:We provide a detailed theoretical analysis of the character of optical transitions and Band Gap Reduction in (Fe1–xCrx)2O3 solid solutions using extensive periodic model and embedded cluster calculations. Time-dependent density functional theory is used to calculate and assign optical absorption Bands for x = 0.0, 0.5, and 1.0 and photon energies up to 5 eV. Consistent with recent experimental data, a Band Gap Reduction of as much as 0.7 eV with respect to that of pure α-Fe2O3 is found. This result is attributed predominantly to two effects: (i) the higher valence Band edge for x ≈ 0.5, as compared to those in pure α-Fe2O3 and α-Cr2O3, and (ii) the onset of Cr → Fe d–d excitations in the solid solutions. Broadening of the valence Band due to hybridization of O 2p with Fe and Cr 3d states also contributes to Band Gap Reduction.
Viktor N Staroverov - One of the best experts on this subject based on the ideXlab platform.
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Band Gap Reduction in zno and zns by creating layered zno zns heterostructures
Journal of Physical Chemistry Letters, 2015Co-Authors: Amin Torabi, Viktor N StaroverovAbstract:Wurtzite-type zinc oxide (ZnO) and zinc sulfide (ZnS) have electronic Band Gaps that are too large for light-harvesting applications. Using screened hybrid density-functional methods, we show that the Band Gaps of ZnO and ZnS can be dramatically reduced by creating layered ZnO/ZnS bulk heterostructures in which m contiguous monolayers of ZnO alternate with n contiguous monolayers of ZnS. In particular, the Band Gap decreases by roughly 40% upon substitution of every tenth monolayer of ZnS with a monolayer of ZnO (and vice versa) and becomes as low as 1.5 eV for heterostructures with m = 3 to m = 9 contiguous monolayers of ZnO alternating with n = 10 – m monolayers of ZnS. The predicted Band Gaps of layered ZnO/ZnS heterostructures span the entire visible spectrum, which makes these materials suitable for photovoltaic device engineering.
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Band Gap Reduction in ZnO and ZnS by Creating Layered ZnO/ZnS Heterostructures
Journal of Physical Chemistry Letters, 2015Co-Authors: Amin Torabi, Viktor N StaroverovAbstract:Wurtzite-type zinc oxide (ZnO) and zinc sulfide (ZnS) have electronic Band Gaps that are too large for light-harvesting applications. Using screened hybrid density-functional methods, we show that the Band Gaps of ZnO and ZnS can be dramatically reduced by creating layered ZnO/ZnS bulk heterostructures in which m contiguous monolayers of ZnO alternate with n contiguous monolayers of ZnS. In particular, the Band Gap decreases by roughly 40% upon substitution of every tenth monolayer of ZnS with a monolayer of ZnO (and vice versa) and becomes as low as 1.5 eV for heterostructures with m = 3 to m = 9 contiguous monolayers of ZnO alternating with n = 10 – m monolayers of ZnS. The predicted Band Gaps of layered ZnO/ZnS heterostructures span the entire visible spectrum, which makes these materials suitable for photovoltaic device engineering.
Scott A Chambers - One of the best experts on this subject based on the ideXlab platform.
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Band Gap Reduction and dopant interaction in epitaxial la cr co doped srtio3 thin films
Chemistry of Materials, 2014Co-Authors: Ryan B Comes, Peter V Sushko, Steve M Heald, Robert J Colby, Mark E Bowden, Scott A ChambersAbstract:We show that by co-doping SrTiO3 (STO) epitaxial thin films with equal amounts of La and Cr, it is possible to produce films with an optical Band Gap ∼0.9 eV lower than that of undoped STO. Sr1–xLaxTi1–xCrxO3 thin films were deposited by molecular beam epitaxy and characterized using X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy to show that the Cr dopants are almost exclusively in the Cr3+ oxidation state. Extended X-ray absorption fine structure measurements and theoretical modeling suggest that it is thermodynamically preferred for La and Cr dopants to occupy nearest-neighbor A- and B-sites in the lattice. Transport measurements show that the material exhibits variable-range hopping conductivity with high resistivity. These results create new opportunities for the use of doped STO films in photovoltaic and photocatalytic applications.
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optical absorption and Band Gap Reduction in fe1 xcrx 2o3 solid solutions a first principles study
Journal of Physical Chemistry C, 2013Co-Authors: Yong Wang, Kenneth Lopata, Scott A Chambers, Niranjan Govind, Peter V SushkoAbstract:We provide a detailed theoretical analysis of the character of optical transitions and Band Gap Reduction in (Fe1–xCrx)2O3 solid solutions using extensive periodic model and embedded cluster calculations. Time-dependent density functional theory is used to calculate and assign optical absorption Bands for x = 0.0, 0.5, and 1.0 and photon energies up to 5 eV. Consistent with recent experimental data, a Band Gap Reduction of as much as 0.7 eV with respect to that of pure α-Fe2O3 is found. This result is attributed predominantly to two effects: (i) the higher valence Band edge for x ≈ 0.5, as compared to those in pure α-Fe2O3 and α-Cr2O3, and (ii) the onset of Cr → Fe d–d excitations in the solid solutions. Broadening of the valence Band due to hybridization of O 2p with Fe and Cr 3d states also contributes to Band Gap Reduction.
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Optical Absorption and Band Gap Reduction in (Fe1–xCrx)2O3 Solid Solutions: A First-Principles Study
Journal of Physical Chemistry C, 2013Co-Authors: Yong Wang, Kenneth Lopata, Scott A Chambers, Niranjan Govind, Peter V SushkoAbstract:We provide a detailed theoretical analysis of the character of optical transitions and Band Gap Reduction in (Fe1–xCrx)2O3 solid solutions using extensive periodic model and embedded cluster calculations. Time-dependent density functional theory is used to calculate and assign optical absorption Bands for x = 0.0, 0.5, and 1.0 and photon energies up to 5 eV. Consistent with recent experimental data, a Band Gap Reduction of as much as 0.7 eV with respect to that of pure α-Fe2O3 is found. This result is attributed predominantly to two effects: (i) the higher valence Band edge for x ≈ 0.5, as compared to those in pure α-Fe2O3 and α-Cr2O3, and (ii) the onset of Cr → Fe d–d excitations in the solid solutions. Broadening of the valence Band due to hybridization of O 2p with Fe and Cr 3d states also contributes to Band Gap Reduction.
Amin Torabi - One of the best experts on this subject based on the ideXlab platform.
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Band Gap Reduction in zno and zns by creating layered zno zns heterostructures
Journal of Physical Chemistry Letters, 2015Co-Authors: Amin Torabi, Viktor N StaroverovAbstract:Wurtzite-type zinc oxide (ZnO) and zinc sulfide (ZnS) have electronic Band Gaps that are too large for light-harvesting applications. Using screened hybrid density-functional methods, we show that the Band Gaps of ZnO and ZnS can be dramatically reduced by creating layered ZnO/ZnS bulk heterostructures in which m contiguous monolayers of ZnO alternate with n contiguous monolayers of ZnS. In particular, the Band Gap decreases by roughly 40% upon substitution of every tenth monolayer of ZnS with a monolayer of ZnO (and vice versa) and becomes as low as 1.5 eV for heterostructures with m = 3 to m = 9 contiguous monolayers of ZnO alternating with n = 10 – m monolayers of ZnS. The predicted Band Gaps of layered ZnO/ZnS heterostructures span the entire visible spectrum, which makes these materials suitable for photovoltaic device engineering.
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Band Gap Reduction in ZnO and ZnS by Creating Layered ZnO/ZnS Heterostructures
Journal of Physical Chemistry Letters, 2015Co-Authors: Amin Torabi, Viktor N StaroverovAbstract:Wurtzite-type zinc oxide (ZnO) and zinc sulfide (ZnS) have electronic Band Gaps that are too large for light-harvesting applications. Using screened hybrid density-functional methods, we show that the Band Gaps of ZnO and ZnS can be dramatically reduced by creating layered ZnO/ZnS bulk heterostructures in which m contiguous monolayers of ZnO alternate with n contiguous monolayers of ZnS. In particular, the Band Gap decreases by roughly 40% upon substitution of every tenth monolayer of ZnS with a monolayer of ZnO (and vice versa) and becomes as low as 1.5 eV for heterostructures with m = 3 to m = 9 contiguous monolayers of ZnO alternating with n = 10 – m monolayers of ZnS. The predicted Band Gaps of layered ZnO/ZnS heterostructures span the entire visible spectrum, which makes these materials suitable for photovoltaic device engineering.
A Mascarenhas - One of the best experts on this subject based on the ideXlab platform.
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Physics of Isoelectronic Dopants in GaAs
Dilute Nitride Semiconductors, 2020Co-Authors: A Mascarenhas, S. Francoeur, S. YoonAbstract:Publisher Summary This chapter introduces the alloy induced splitting of the L6o conduction Band with semi-conductor. This transition optically is forbidden in pure III-V alloys, and results from the strong perturbation caused by the impurity potential of nitrogen that hosts Band structure of GaAs. The perturbation creates disorder strong enough to reduce the symmetry of the system, lift the degeneracy of the L-points, and generates a non-vanishing transition probability between the a1(l) singlet and the valence Band maximum. Therefore, intra-Band coupling between all conduction Band singlet states, but predominantly between al(l) and al(l), underlies the Band Gap Reduction observed for GaAsN. This effect, observed in all semiconductor alloys and quantified by the bowing co-efficient, is profound enough in GaAsN to create a non-monotonic dependence of the Band Gap as a function of nitrogen concentration. The large Band Gap Reduction of GaAs resulting from a small concentration of Bismuth (Bi) is also a potential candidate for near-infrared emitters, especially when mixed with nitrogen to form a GaAsNBi alloy.
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Electronic structure of heavily and randomly nitrogen doped GaAs near the fundamental Band Gap
Physica Status Solidi B-basic Solid State Physics, 2001Co-Authors: Yong Zhang, A Mascarenhas, Sebastien Francoeur, C W TuAbstract:On increasing the nitrogen doping concentration in GaAs, states associated with isolated, paired and clustered (i.e., more complex configurations) nitrogen atoms sequentially appear, with their energy levels being resonant for the isolated center and most of the pairs and becoming bound for a couple of pairs and clusters. At a nitrogen mole concentration of x ∼ 0.1%, the shallow nitrogen bound states have merged with the GaAs Band edge, which effectively gives rise to a Band Gap Reduction, but the deeper nitrogen bound states persist as discrete levels. We study the behavior of nitrogen at this transition concentration, using various techniques (photoluminescence under selective excitation, electroreflectance, and Raman scattering), in order to gain insight into the large Band Gap Reduction observed at all nitrogen concentrations. The validity of a few existing models proposed for explaining the large Band Gap Reduction will be briefly discussed.
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Optical transitions in the isoelectronically doped semiconductor Gap:N: An evolution from isolated centers, pairs, and clusters to an impurity Band
Physical Review B, 2000Co-Authors: Yong Zhang, A Mascarenhas, Brian Fluegel, C W TuAbstract:In heavily nitrogen doped Gap, we show how isoelectronic doping results in an impurity Band, and how this is manifested as a large Band-Gap Reduction and an enhanced Band-edge absorption. Heavily doped Gap:N or Gap{sub 1-x}N{sub x} exhibits properties characteristic of both direct and indirect Gap semiconductors. Exciton bound states associated with perturbed nitrogen pair centers and larger GaN clusters are observed. This paper indicates that to properly describe the properties of an impurity Band, a hierarchy of impurity complexes needs to be considered. Our data also suggest that the excitonic effect plays a role in the impurity Band formation and Band-Gap Reduction. (c) 2000 The American Physical Society.
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Nitrogen-Activated Transitions, Level Repulsion, and Band Gap Reduction in GaAs{sub 1{minus}x}N{sub x } with x {lt} 0.03
Physical Review Letters, 1999Co-Authors: John D. Perkins, J. M. Olson, Yong Zhang, A Mascarenhas, John F. Geisz, Daniel J. Friedman, Sarah KurtzAbstract:We report electroreflectance spectra for a series of GaAs{sub 1{minus}x} N{sub x} samples with x{lt}0.03 . For all samples, the fundamental Band Gap transition (E{sub 0}) and the transition from the spin-orbit split-off valence Band (E{sub 0}+{Delta}{sub 0}) are observed. For samples with x{ge}0.008 , an additional transition (E{sub +}) is observed. With increasing nitrogen content, the increase in E{sub +} is linear in, and nearly equal to, the Band Gap Reduction indicative of a nitrogen-induced level repulsion. The directly observed E{sub +} transition may arise from either a nitrogen-related resonant level or a disorder-activated indirect transition. {copyright} {ital 1999} {ital The American Physical Society}
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X-RAY DIFFRACTION AND EXCITATION PHOTOLUMINESCENCE ANALYSIS OF ORDERED GAINP
Physical Review B, 1998Co-Authors: R. L. Forrest, P Ernst, Yong Zhang, A Mascarenhas, John F. Geisz, T. D. Golding, Simon C. Moss, Jerry M. Olson, C GengAbstract:X-ray diffraction is shown to provide a direct, quantitative, structural measurement of the degree of spontaneous ordering in GaInP. In this paper we combine x-ray diffraction and excitation photoluminescence analyses of CuPt-ordered GaInP, and comparing the results to theoretical predictions for the dependence of the Band structure on order parameter, determine the values of the Band-Gap Reduction and crystal-field splitting parameters for the perfectly ordered alloy. {copyright} {ital 1998} {ital The American Physical Society}