Highly transparent and conductive Ga-doped ZnO films with good thermal stability prepared by dual-target reactive sputtering

Generally, Zn-Ga metal alloy or ZnO-Ga₂O₃ ceramic is used as the sputtering target for the preparation of Ga-doped ZnO (GZO) films. However, it is often difficult or expensive to obtain Ga heavily doped ZnO films with good optoelectronic properties. In this article, GZO films were deposited by both DC sputtering of zinc target and RF sputtering of Ga₂O₃ target for the first time. It was studied for the influences of the sputtering power of Ga₂O₃ target varied from 0 to 150 W. Moreover, the thermal stability of the as-deposited GZO films was analyzed. The GZO films have a hexagonal wurtzite structure with (0 0 2) preferred orientation. The Ga doping increases with the Ga₂O₃ power, in which the maximum doping amount reaches 6.5 at%. However, when the power is 130 W, the GZO film has the highest carrier concentration of 2.4×10²¹ cm^-3 and the lowest resistivity of 2.2×10^-4 Ω cm, while remains high visible average transmittance of 85.3%. Furthermore, our developed GZO films can maintain highly transparent conductive performance even after annealing at elevated temperature (up to 500 °C).