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Publisher: New York : American Institute of Physics Ă— Subject: Electronic bandstructure Ă—

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    Schottky 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.
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    Anisotropic 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, RĂ¼diger
    The 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.