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Author: Bierwagen, O. × End date: 2019 ×

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Now showing 1 - 3 of 3
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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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    Valence-band density of states and surface electron accumulation in epitaxial SnO2 films
    (College Park : American Physical Society, 2014) Vasheghani Farahani, S.K.; Veal, T.D.; Mudd, J.J.; Scanlon, D.O.; Watson, G.W.; Bierwagen, O.; White, M.E.; Speck, J.S.; McConville, C.F.
    The surface band bending and electronic properties of SnO2(101) films grown on r-sapphire by plasma-assisted molecular beam epitaxy have been studied by Fourier-transform infrared spectroscopy (FTIR), x-ray photoemission spectroscopy (XPS), Hall effect, and electrochemical capacitance-voltage measurements. The XPS results were correlated with density functional theory calculation of the partial density of states in the valence-band and semicore levels. Good agreement was found between theory and experiment with a small offset of the Sn 4d levels. Homogeneous Sb-doped SnO2 films allowed for the calculation of the bulk Fermi level with respect to the conduction-band minimum within the k⋅p carrier statistics model. The band bending and carrier concentration as a function of depth were obtained from the capacitance-voltage characteristics and model space charge calculations of the Mott-Schottky plots at the surface of Sb-doped SnO2 films. It was quantitatively demonstrated that SnO2 films have downward band bending and surface electron accumulation. The surface band bending, unoccupied donor surface-state density, and width of the accumulation region all decrease with increasing Sb concentration.
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    Electrical conductivity and gas-sensing properties of Mg-doped and undoped single-crystalline In2O3 thin films: Bulk vs. surface
    (Amsterdam : Elsevier, 2015) Rombach, J.; Bierwagen, O.; Papadogianni, A.; Mischo, M.; Cimalla, V.; Berthold, T.; Krischok, S.; Himmerlich, M.
    This study aims to provide a better fundamental understanding of the gas-sensing mechanism of In2O3-based conductometric gas sensors. In contrast to typically used polycrystalline films, we study single crystalline In2O3 thin films grown by molecular beam epitaxy (MBE) as a model system with reduced complexity. Electrical conductance of these films essentially consists of two parallel contributions: the bulk of the film and the surface electron accumulation layer (SEAL). Both these contributions are varied to understand their effect on the sensor response. Conductance changes induced by UV illumination in air, which forces desorption of oxygen adatoms on the surface, give a measure of the sensor response and show that the sensor effect is only due to the SEAL contribution to overall conductance. Therefore, a strong sensitivity increase can be expected by reducing or eliminating the bulk conductivity in single crystalline films or the intra-grain conductivity in polycrystalline films. Gas-response measurements in ozone atmosphere test this approach for the real application.