Carrier transport in nanoporous TiO2 films

Recent results on electron transport in nanoporous TiO2 films with gas-fill ed, insulating pores are evaluated. Measurements on Pt/TiO2 Schottky barrie r structures indicate a barrier height of 1.7 eV, compatible with an electr on affinity of 3.9 eV for the TiO2 films. Below similar to 300 K, tunneling transport through the barrier occurs, resulting in barrier lowering effect s. Carrier drift mobilities, recombination lifetimes and their dependence o n injection level in TiO2 are reported. It is found that the mobility-lifet ime product is independent of injection level, while drift mobility and rec ombination lifetime change strongly with injection. All experimental findin gs are discussed in terms of two different transport models, one based on t rap filling, the other on the screening of potential fluctuations. The trap filling model appears as the more plausible model. Comparison with recent experiments on nanoporous films in contact with electrolytes indicate that the transport and recombination mechanism is qualitatively similar for the two cases.