Thermal activation of the electronic transport in porous titanium dioxides

The thermal activation of the electronic transport in sintered nanoporous TiO2 (anatase, rutile) layers has been investigated by current voltage characteristics, impedance spectroscopy and time of flight techniques. The thermal activation energy of the electrical conductivity and drift mobility is about 0.8 eV independent of the phase of the titanium dioxide, the diameter of the TiO2 nanocrystals and of the absolute value of the electrical conductivity. We propose a model which describes the electron transport in a sintered nanoporous TiO2 network as limited by traps located in the small contact regions of the grains. Dielectric screening is discussed as a possible reason for the increase of the energy of defect levels near the conduction band which determine the Fermi-level position.