Structural, optical and electrical properties of sputtered Nb doped TiO2 transparent conductive films

Sputtered TNO films with various thicknesses were prepared and post-annealed by single step (vacuum or O2) and dual steps (vacuum + O2 or O2 + vacuum) at 300 °C. The TNO films (20–110 nm) with vacuum annealing are polycrystalline and conductive. After treated by vacuum + O2 annealing, thick TNO films (40–110 nm) exhibit O-poor state with low resistivity in comparison with insulating 20 nm TNO film. In contrast, the TNO films treated by O2 or O2 + vacuum annealing are insulating or with large resistivity. Besides, the vacuum annealed 20 nm TNO film presents abnormal properties, such as larger lattice constant and lower optical band gap, which is probably induced by the stress from substrates or grains.