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 105Ωcm. A slight oxygen deficiency in as-deposited films was essential to gain low resistivities (10−3Ωcm) and low optical absorption coefficients (α550nm<2×103cm−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>1020cm−3) increased with decreasing substrate temperature owing to metal-like phonon scattering in these samples. •Slight oxygen deficient as-deposited films were highly conductive after annealing.•Control of oxygen stoichiometry by adjusting the discharge voltage during deposition•Electron mobility at room temperature is limited due to scattering at phonons.•Films exhibited large average crystallite sizes with planar structural defects.