Thermal activation of the electronic transport in porous titanium dioxides

The thermal activation of the electronic transport in sintered nanoporous T iO2 (anatase, rutile) layers has been investigated by current voltage chara cteristics, impedance spectroscopy and time of flight techniques. The therm al activation energy of the electrical conductivity and drift mobility is a bout 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 conduc tivity. We propose a model which describes the electron transport in a sint ered nanoporous TiO2 network as limited by traps located in the small conta ct regions of the grains. Dielectric screening is discussed as a possible r eason for the increase of the energy of defect levels near the conduction b and which determine the Fermi-level position. (C) 2000 Elsevier Science S.A . All rights reserved.