DOPING EFFECTS IN WIDE GAP OXIDE FILMS

Oxide-based films and nanostructures have emerged as important and promising materials for a wide range of applications such as photovoltaics, photocatalysis, optoelectronics, gas sensing and electronics. Many of these technologies require the use of transparent electrodes and charge collectors. At present, indium tin oxide (ITO) is the commonly large scale manufactured and used material. Many materials are under study to replace the costly and scarce ITO. The doping effects of cheaper and more abundant materials Niobium-doped TiO2 films were produced by RF co-sputtering of a TiO2 in argon, argon-H2 and argon-O2 plasmas, followed by vacuum thermal annealing. In view of application in the photovoltaics field, new materials are also explored and developed to increase the conversion efficiency of solar cells through the increase of the most efficient and useful fraction of the solar spectrum which hits the cells, thanks to spectrum conversion processes such as frequency down-shifting conversion. In that sense, the development of oxides doped with rare earths offers new opportunities to realize active materials for the efficient absorption and conversion of the solar radiation in solar cell. In this view, wide band gap oxide films doped with rare earth ions able to insure such processes were synthesized. To develop an appropriate understanding of the properties of the doped oxide films, it is necessary to address the material preparation methods and also structural and defect issues. The effect of doping on the optical properties of the films was studied. A combined use of optical and x-ray photoemission spectroscopies provided information about the electronic properties of the films. Fundamental properties regarding the valence band, the Fermi level and the work function of the un-doped and doped films were studied