Grundlegende Untersuchungen zu In2O3 Einkristallen

This thesis deals with investigations of the electronic structure, transport properties and the doping of In2O3 single crystals belonging to the group of the transparent conducting oxides (TCO’s). The physics of these solids was not well understood when starting this thesis or was at least discussed controversially. Therefore details of the electronic structure of In2O3 were examined by means of high-resolution angle resolved photoelectron spectroscopy (ARPES) using synchrotron radiation. Fundamentally the properties of a degenerate n-type semiconductor with direct band gap could be obtained by measurements on in situ cleaved single crystal surfaces. This is remarkable with regard to published results on thin films, where in many cases two dimensional charge accumulation layers were found on the surface. Moreover important parameters as the size of the band gap and the effective masses of valence and conduction band could be determined. The Fermi surface could be investigated as a three dimensional object in momentum space. Especially the ARPES measurements at low photon energies revealed additionally a series of band gap states, which were discussed as defect states in the context to doping. The influence of polaronic interactions on the spectral function was proven in the region of the Fermi energy for the first time. To gain access to the intrinsic properties of In2O3 single crystals were self grown by means of chemical vapour transport (CVT) and characterized. The stoichiometric composition of In2O3 crystals was examined with the help of energy dispersive X-ray spectroscopy (EDX) and the crystalline structure and the lattice parameters were determined by means of X-ray diffraction. The transport properties such as specific resistivity, charge carrier density and mobility were determined by means of a four-contact method and Hall-effect measurements (five-contact method), which confirmed the nconducting character of In2O3. Furthermore, the effect of the annealing in oxygen flow as well as the effect of storage in air on the transport properties of the crystals and was examined and described. The band gap states were also measured by means of scanning tunneling spectroscopy (STS). The energy positions of the gap states were determined and compared with the photoelectron spectroscopy data. Nearly identical quantitative consistence was observed. In addition, the band gap states obtained from these two methods of measurement were compared with the theoretical predictions of the electronic structure and with the reported results of In2O3 thin films.