Co-sputtered tantalum-doped tin oxide thin films for transparent conducting applications

A transparent conducting material combines high electrical conductivity with high optical transparency. Such materials are actively sought for their applications in optoelectronic devices and consumer electronics. Undoped tin oxide is a wide-bandgap semiconductor that is optically transparent in the visible range but lacks the electrical conductivity necessary for its function as a transparent conductor. In this study, conductive tin oxide thin films were obtained through extrinsic doping with tantalum, which is considered one of the best dopants due to its oxidation state and smaller ionic radius than that of tin. The films were deposited by co-sputtering; radio-frequency sputtering was applied to tin oxide, and then variable-power direct-current sputtering was applied to tantalum to achieve films with tantalum concentrations in the range of 2.6–15.5 at%. The resulting films were highly transparent, with a bandgap in the range of 4.1–4.2 eV and a minimum electrical resistivity of 2.44 × 10−3 Ω cm, corresponding to a Hall mobility of 8.62 cm2/V⋅s. The suitability of these films as transparent conductors was evaluated.