Niobium-doped TiO2 films as highly transparent conducting oxides for electrical contacts were investigated. As-deposited films were amorphous and exhibited high resistivities ranging from 10 to 10(5) Omega cm. A slight oxygen deficiency in as-deposited films was essential to gain low resistivities (10(-3) Omega cm) and low optical absorption coefficients (alpha(550 nm) < 2 x 10(3) cm(-1)) in the annealed films. Therefore, we controlled the oxygen stoichiometry during the film deposition by adjusting the magnetron discharge voltage, while the oxygen gas flow was kept constant. The Hall mobility of degenerately doped films (electron concentration > 10(20) cm(-3)) increased with decreasing substrate temperature owing to metal-like phonon scattering in these samples. (C) 2015 Elsevier B.V. All rights reserved.