Influence of intrinsic defects on the electrical and optical properties of TiO2:Nb films sputtered at room temperature

Abstract

Oxide-based films and nanostructures have emerged as important materials for a wide range of applications such as photovoltaics, optoelectronics, gas sensing and electronics. To develop an appropriate understanding of the properties of these oxides, it is necessary to address the material preparation methods and defect probing issues. This work reports on the synthesis processes of TiO2 based transparent conductive films, their stoichiometry control and defect identifying, in relation with their electrical and optical properties. Un-doped and TiO2:Nb films were deposited by RF co-sputtering from TiO2 and Nb2O5 targets in Ar plasma. The chemical species present in the plasmas used in deposition process were investigated by optical emission spectroscopy, which was later on correlated with the defects structure of the films. Analysis by X-ray photoelectron spectroscopy shed more light on the nature of the vacancies and on the effect of the latter on the optical and electrical properties of the films. In terms of results, we measured electrical resistivity in the range 10−2–10−3Ωcm for the intrinsically and extrinsically doped films (films doped with oxygen vacancies and Nb+5 respectively) while the lowest resistivity was obtained for intrinsically-extrinsically co-doped TiO2 films (7.4×10−4Ωcm). The films transparency was also actively determined by the defects in the lattice and highly transparent films (65–85% in the visible range) were obtained by controlling the density of defects. The approach adopted in this work for the generation of oxygen vacancies could be useful for other oxide-based films, where the oxygen vacancies-dependent properties are crucial, for room temperature ferromagnetism and photocatalytic applications.