نبذة مختصرة : This study is concerned with correlating the macroscopic optoelectronic properties of SnO2 tin oxide, a transparent conducting oxide, with its microscopic morphology and electronic structure. To this end, a set of around 300 thin film samples was synthesized by sputter deposition and thoroughly characterised using state of the art analytical methods, first and foremost in-situ photoelectron spectroscopy. One main topic of the work is the correct determination of Fermi level position, and extraction of further meaningful physical information, from X-ray photoelectron spectroscopy (XPS) data. Comparison with charge carrier density, determined by Hall-effect measurement, indicates that the usually employed approaches are not suited to extract Fermi level positions from XPS data, due to doped SnO2 being a degenerate semiconductor. A more elaborate approach is successfully developed. SnO2 Fermi Level positions are then used to analyse the correlation of optoelectronic properties of SnO2 thin films doped with Antimony or Tantalum with their microscopic morphology. Results indicate that energetic barriers, caused by band bending at grain boundaries, are limiting factors in regard to electrical conductivity. Band bending at grain boundaries and surfaces is analysed thoroughly by using XPS and electrical measurements, developing new data analysis methods in the process. These methods are then employed to prove the validity of a novel doping concept called 'insulator modulation doping', which uses the band alignment at an Al2O3-SnO2 interface to locally force the SnO2 Fermi level above the classical doping limit, which has previously not been thought to be possible.
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