Polaron transport in TiO2 thin films

Undoped and Fe-doped TiO2 thin films were obtained by rf-sputtering technique onto heated glass substrates (250 degrees C) covered with indium tin oxide. The temperature dependence of the electrical conductivity was investigated in the temperature range 13-320 K, and it shows that the conduction mechanism in the studied samples is described by small-polaron hopping (SPH) at temperatures higher than half of the Debye temperature (theta(D)). It was found that the magnitude of the SPH coupling increases by Fe doping in TiO2 thin films. With decreasing temperature, the conduction behavior transited from SPH conduction to variable-range hopping (VRH) conduction. In the intermediate temperature domain (200 K<T<theta(D)/2), the VRH conduction was found to be dominant, while a temperature-independent conductivity behavior was observed in the lower temperature range (T<200 K). (C) 2010 American Institute of Physics. [doi: 10.1063/1.3493742]