Electronic structure, transport properties and doping of wide-band gap semiconducting oxides NixMg1-xO and BaSnO3

• Main Author: Niedermeier, Christian Alexander
• Other Authors: Moram, Michelle A. ; Alford, Neil
• Published: Imperial College London 2016
• Subjects: 621.3815
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.726932

Wide-band gap semiconducting oxides combine high electrical conductivity with optical transparency and find important applications as transparent contacts in solar cells, energy-efficient smart windows and thin film transistors used in flat-panel displays for smartphones and tablets. Among the material family of transparent conducting oxides, In2O3, SnO2, ZnO and CdO are the most prominent examples which all exhibit excellent n-type conductivity. Transition metal oxides such as Cu2O, CuAlO2 and NiO were investigated for their p-type conductivity, which remains a great challenge to achieve in oxide semiconductors. This thesis presents an investigation of the electronic structure and transport properties of NixMg1-xO, a fully miscible solid solution of NiO and MgO which allows for band gap tuning in the deep ultraviolet spectral region. Both materials crystallize in the cubic rock-salt structure with nearly identical lattice parameters, but their alloys exhibit an unusually large, non-parabolic band gap bowing which has led to controversial discussions in the literature. The second part of this thesis focusses on the thin film crystal growth, the electron transport properties and doping in the ideal cubic perovskite BaSnO3, which recently attracted significant interest as high-mobility electron transport material for oxide electronics composed of earth-abundant elements. An effective solid phase epitaxy method for preparation of high-mobility La:BaSnO3 films is developed, employing the room temperature-deposited nanocrystalline films as precursor. Furthermore, the first experimental report of interstitial H-doping of BaSnO3 films is demonstrated, presenting a promising n-type doping alternative for achieving excellent conductivity. Finally, the origin of the exceptionally high room temperature mobility is investigated through an in-depth characterization of the electron effective mass and carrier scattering mechanisms in epitaxial La:BaSnO3 thin films.