Thin-film polycrystalline titanium-oxygen semiconductors prepared by spray pyrolysis
Spray-pyrolytic preparation of thin-film polycrystalline KTiOPO 4, RbTiOPO4, TiO2 and BaTiO3 is reported. A peroxo-hydroxo complex of titanium was used as a precursor, and its synthesis has been optimized. An analogous complex of niobium has been prepared and used as a precursor for the first time; other transition metals can be used as well. The stoichiometric, crack-free films of controlled thickness were grown on a variety of substrates. Depending on deposition temperature, either highly porous or dense films were obtained. A deposition mechanism is suggested based on the observed temperature dependence. The effects of annealing on the crystal structure of the materials were studied. Bandgap values were calculated from the optical absorption data. Electronic properties of the materials have been explored by long-time transient photoconductivity, Hall effect and complex impedance measurements. From the photoconductivity data, density-of-states distribution of the hole sensitizing centres in the lower third of the bandgap has been obtained and related to reversible oxygen adsorption at the surface.