Polycrystalline In₂O₃ thin films have great potential for low cost and low energy consumption environmental sensors, e.g. for the detection of ozone. We have examined the properties of indium oxide thin films (In₂O₃) prepared by metal organic chemical vapour deposition using X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS), electron energy loss spectroscopy (EELS), atomic force microscopy (AFM) and high resolution transmission microscopy (HRTEM). The growth of In₂O₃ was performed on Al₂O₃(0001) in a horizontal MOCVD reactor using trimethylindium and H₂O vapour as precursors and N₂ as carrier gas. The influence of the growth temperature and rate on structure, morphology, stoichiometry as well as the surface electronic properties has been investigated. A dependence of the core level binding energy and the valence band density of states on the growth temperature is found, induced by changes in the surface band bending linked to differences in the resistivity of the films. For samples grown at low temperature (200°C), strong emission from a state below the valence band maximum, which is to our knowledge unidentified up to date, is observed. Additionally, differences in the XPS, UPS and EELS spectra of bixbyite In₂O₃ and samples with rhombohedral crystal structure are presented and discussed. In order to identify the photoreduction and oxidation mechanisms related to the ozone detection capability of In₂O₃, we have investigated the interaction of indium oxide thin films with O₃ and UV radiation. From the changes of the valence band electron spectra it is concluded that the O₃ interaction is induced by a reversible saturation of defect states at the In₂O₃ surface resulting in adsorption of an oxygen species with two distinct states at 6.1 eV and 11.3 eV in the valence band and an increase of the sample work function.

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