Thin films of 5 and 10-layered sol gel TiO2 were doped with 1.2 at.% Nb and their structural, optical and electrical properties were investigated. The films crystallized only in anatase phase, as evidenced by X-ray diffraction and selected area electron diffraction analyses. High resolution transmission electron microscopy revealed nanosized crystallites with amorphous boundaries. Current-voltage measurements on metal-TiO2 Si structures showed the formation of ri+ n heterojunction at the TiO2-Si interface with a rectification ratio of 10(4). The effective donor density varies between 10(16) and 10(17) cm(-3), depending on film thickness. The sheet energy densities under forward and reverse bias are in the order of 10(12) and 10(10) cm(-2) respectively. These values and the high specific resistivity (10(4) Omega cm) support the existence of compensating acceptor levels in these films. It was established that the conduction mechanism is based on space charge limited current via deep levels with different energy positions in the band gap. (C) 2015 Elsevier Ltd. All rights reserved.