1,557 research outputs found

    Spin-Filtering Multiferroic-Semiconductor Heterojunctions

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    We report on the structural and electronic properties of the interface between the multiferoic oxide YMnO3_3 and wide band-gap semiconductor GaN studied with the Hubbard-corrected local spin density approximation (LSDA+U) to density-functional theory (DFT). We find that the band offsets at the interface between antiferromagnetically ordered YMnO3_3 and GaN are different for spin-up and spin-down states. This behavior is due to the spin splitting of the valence band induced by the interface. The energy barrier depends on the relative orientation of the electric polarization with respect to the polarization direction of the GaN substrate suggesting an opportunity to create magnetic tunnel junctions in this materials system.Comment: 4 pages, 4 figure

    Exciton Regeneration at Polymeric Semiconductor Heterojunctions

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    Control of the band-edge offsets at heterojunctions between organic semiconductors allows efficient operation of either photovoltaic or light-emitting diodes. We investigate systems where the exciton is marginally stable against charge separation, and show via E-field-dependent time-resolved photoluminescence spectroscopy that excitons that have undergone charge separation at a heterojunction can be efficiently regenerated. This is because the charge transfer produces a geminate electron-hole pair (separation 2.2-3.1nm) which may collapse into an exciplex and then endothermically (E=100-200meV) back-transfer towards the exciton.Comment: 10 pages, 4 figures. Manuscript in press in Phys. Rev. Let

    Tight-binding study of interface states in semiconductor heterojunctions

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    Localized interface states in abrupt semiconductor heterojunctions are studied within a tight-binding model. The intention is to provide a microscopic foundation for the results of similar studies which were based upon the two-band model within the envelope function approximation. In a two-dimensional description, the tight-binding Hamiltonian is constructed such that the Dirac-like bulk spectrum of the two-band model is recovered in the continuum limit. Localized states in heterojunctions are shown to occur under conditions equivalent to those of the two-band model. In particular, shallow interface states are identified in non-inverted junctions with intersecting bulk dispersion curves. As a specific example, the GaSb-AlSb heterojunction is considered. The matching conditions of the envelope function approximation are analyzed within the tight-binding description.Comment: RevTeX, 11 pages, 3 figures, to appear in Phys. Rev.

    Study of semiconductor heterojunctions of ZnSe, GaAs and Ge Quarterly report, 1 Aug. - 31 Oct. 1969

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    Semiconductor heterojunctions of zinc selenides, gallium arsenides, and germaniu

    Recent Advances in Semiconductor Heterojunctions and Z-Schemes for Photocatalytic Hydrogen Generation

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    The formation of semiconductor heterojunctions and Z-schemes is still a very prominent and efficient strategy of materials chemists to extend the absorption range of semiconductor combinations. Moreover, the spatial separation of photoexcited charge carriers and thereby the reduction of their recombination ultimately lead to increased photocatalytic activities. The present article reviews recent trends in semiconductor heterojunctions and Z-schemes with a focus on hydrogen generation and water splitting, exhibiting specific needs for charge carrier separation. We also included recent material trends, i.e. 2D/2D combinations, direct Z-schemes, MOFs and COFs, and combinations with upconversion materials

    Schottky barrier heights at polar metal/semiconductor interfaces

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    Using a first-principle pseudopotential approach, we have investigated the Schottky barrier heights of abrupt Al/Ge, Al/GaAs, Al/AlAs, and Al/ZnSe (100) junctions, and their dependence on the semiconductor chemical composition and surface termination. A model based on linear-response theory is developed, which provides a simple, yet accurate description of the barrier-height variations with the chemical composition of the semiconductor. The larger barrier values found for the anion- than for the cation-terminated surfaces are explained in terms of the screened charge of the polar semiconductor surface and its image charge at the metal surface. Atomic scale computations show how the classical image charge concept, valid for charges placed at large distances from the metal, extends to distances shorter than the decay length of the metal-induced-gap states.Comment: REVTeX 4, 11 pages, 6 EPS figure

    Interface relaxation and electrostatic charge depletion in the oxide heterostructure LaAlO3/SrTiO3

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    Performing an analysis within density functional theory, we develop insight into the structural and electronic properties of the oxide heterostructure LaAlO3/SrTiO3. Electrostatic surface effects are decomposed from the internal lattice distortion in order to clarify their interplay. We first study the interface relaxation by a multi-layer system without surface, and the surface effects, separately, by a substrate-film system. While elongation of the TiO6 octahedra at the interface enhances the metallicity, reduction of the film thickness has the opposite effect due to a growing charge depletion. The interplay of these two effects, as reflected by the full lattice relaxation in the substrate-film system, however, strongly depends on the film thickness. An inversion of the TiO6 distortion pattern for films thinner than four LaAlO3 layers results in an insulating state.Comment: 10 pages, 7 figures, accepted by Europhysics Letter
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