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- ItemSchottky contacts to In2O3(New York : American Institute of Physics, 2014) von Wenckstern, H.; Splith, D.; Schmidt, F.; Grundmann, M.; Bierwagen, O.; Speck, J.S.n-type binary compound semiconductors such as InN, InAs, or In2O3 are especial because the branch-point energy or charge neutrality level lies within the conduction band. Their tendency to form a surface electron accumulation layer prevents the formation of rectifying Schottky contacts. Utilizing a reactive sputtering process in an oxygen-containing atmosphere, we demonstrate Schottky barrier diodes on indium oxide thin films with rectifying properties being sufficient for space charge layer spectroscopy. Conventional non-reactive sputtering resulted in ohmic contacts. We compare the rectification of Pt, Pd, and Au Schottky contacts on In2O3 and discuss temperature-dependent current-voltage characteristics of Pt/In2O3 in detail. The results substantiate the picture of oxygen vacancies being the source of electrons accumulating at the surface, however, the position of the charge neutrality level and/or the prediction of Schottky barrier heights from it are questioned.
- ItemAnisotropic optical properties of highly doped rutile SnO2: Valence band contributions to the Burstein-Moss shift(New York : American Institute of Physics, 2018) Feneberg, Martin; Lidig, Christian; White, Mark E.; Tsai, Min Y.; Speck, James S.; Bierwagen, Oliver; Galazka, Zbigniew; Goldhahn, RüdigerThe interband absorption of the transparent conducting semiconductor rutile stannic oxide (SnO2) is investigated as a function of increasing free electron concentration. The anisotropic dielectric functions of SnO2:Sb are determined by spectroscopic ellipsometry. The onsets of strong interband absorption found at different positions shift to higher photon energies with increasing free carrier concentration. For the electric field vector parallel to the optic axis, a low energy shoulder increases in prominence with increasing free electron concentration. We analyze the influence of different many-body effects and can model the behavior by taking into account bandgap renormalization and the Burstein-Moss effect. The latter consists of contributions from the conduction and the valence bands which can be distinguished because the nonparabolic conduction band dispersion of SnO2 is known already with high accuracy. The possible originsof the shoulder are discussed. The most likely mechanism is identified to be interband transitions at jkj > 0 from a dipole forbidden valence band.
- ItemMultiband k $cdot$ p model and fitting scheme for ab initio-based electronic structure parameters for wurtzite GaAs(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2020) Marquardt, Oliver; Caro, Miguel A.; Koprucki, Thomas; Mathé, Peter; Willatzen, MortenWe develop a 16-band k · p model for the description of wurtzite GaAs, together with a novel scheme to determine electronic structure parameters for multiband k · p models. Our approach uses low-discrepancy sequences to fit k · p band structures beyond the eight-band scheme to most recent ab initio data, obtained within the framework for hybrid-functional density functional theory with a screened-exchange hybrid functional. We report structural parameters, elastic constants, band structures along high-symmetry lines, and deformation potentials at the Γ point. Based on this, we compute the bulk electronic properties (Γ point energies, effective masses, Luttinger-like parameters, and optical matrix parameters) for a ten-band and a sixteen-band k · p model for wurtzite GaAs. Our fitting scheme can assign priorities to both selected bands and k points that are of particular interest for specific applications. Finally, ellipticity conditions can be taken into account within our fitting scheme in order to make the resulting parameter sets robust against spurious solutions.