Dark conductivity and transient photoconductivity of nanocrystalline undoped and N-doped TiO2 sol–gel thin films

The dark conductivity and transient photoconductivity of undoped and N-doped porous, sol–gel thin TiO2 films were studied in vacuum and in air. The dark conductivity of the undoped samples is higher in air and this effect is attributed to adsorbed water. For the N-doped samples, the heavier doping causes a high increase in the dark conductivity, while the presence of Nitrogen somehow prevents the water adsorption in air. The photoconductivity reaches very high values and is sensitive on the environment. The presence of Nitrogen decreases dramatically the photoconductivity and increases significantly the saturating as well as the decay times.