Influence of annealing process on conductive properties of Nb-doped TiO2 polycrystalline films prepared by sol–gel method

Nb-doped TiO2 (TNO) thin films were prepared by sol–gel dip-coating method with Nb content in a wide range of 0–20 at.%. The prepared films were preheated at 400 °C and then undertaken by two different post-annealing processes: (a) three times vacuum annealing and (b) multi-round annealing. The designed multi-round annealing was shown to be an effective way to improve the conductive properties of the films, compared to the traditional vacuum annealing process. The minimum resistivity reached approximately 0.5 Ω cm with Nb doping concentration around 12 at.%, and the carrier density increased with Nb-doping concentration until the critical point of 12 at.%, which might be the optimal doping content for our TNO films prepared by sol–gel method.