Structural, optical and electrical characterization of ITO films co-doped with Molybdenum

In this paper we report a detailed investigation on the structural, electrical, and optical properties of Mo-doped ITO (ITMO) thin films. ITMO was deposited at room temperature by RF magnetron co-sputtering from ITO and Mo targets, and also thermal annealed up to 500 °C after the growth. The analyses revealed a high doping efficiency of the Mo already at room temperature. Moreover, a strong improvement of the electrical and optical properties is observed after thermal process. In particular, at T ≥ 300 °C, a drastic enhancement of the optical transparency in the visible and near-IR region was found, accompanied by a strong lowering of the electrical resistivity. The effects with temperature can be ascribed to the annealing of structural defects, as demonstrated by the Tauc's optical analysis and by the enhancement of the carrier mobility. XPS analyses give evidence of the preferential formation of the Mo6+ (MoO3) with respect to the Mo4+ (MoO2) and Mo0 (metallic Mo) oxidation states. These results confirm the important role of Mo as dopant or co-dopant of In oxide based TCO.