Structures and Physical Properties of Films Deposited by Simultaneous DC Sputtering of ZnO and In2O3 or ITO Targets

Oxide films in the ZnO–In2O3 and ZnO–tin-doped indium oxide (ITO) systems were deposited by simultaneous dc sputtering of ZnO and In2O3 or ITO facing targets at substrate temperatures from room temperature up to 300°C. The ratio δ of the ZnO target current to the sum of both the currents was varied. The bixbyite-type In2O3 phase, an amorphous phase, the homologous ZnkIn2Ok+3 phases, and the wurtzite-type ZnO phase were found in this order with increasing δ values. Characteristic trends were observed for δ-dependent electrical properties within the respective phase groups, regardless of the substrate temperatures. The minimum resistivity of 2.3×10−4 Ω cm and the maximum carrier concentration of 1.2×1021 cm−3 were obtained for the amorphous film deposited at 150°C and δ=0.20, having the atomic ratio of [Zn]/([In]+[Zn])=0.22. Sn doping was effective in improving the electrical properties only in the region where the bixbyite-type In2O3 phase appeared and was less effective in the amorphous, homologous ZnkIn2Ok+3 and wurtzite-type ZnO regions.