Superimposed RF/DC magnetron sputtering of transparent Ga:ZnO with high conductivity for photovoltaic contacts applications

Transparent conducting oxides (TCOs) based on gallium-doped ZnO (GZO) are deposited using a radio-frequency (RF) superimposed direct current (DC) magnetron system. The electrical, optical, and structural properties of GZO films deposited by varying the RF/DC power ratio are presented. Our results indicate an increase in conductivity of GZO films up to 3800 S/cm when grown in a pure argon atmosphere at an RF/DC power ratio of 1:1. Optical transmittance for all films is ~90% in the visible range. We find our high-conductivity samples to be highly textured wurtzite ZnO with the c-axis oriented perpendicular to the substrate. The films are relatively smooth with root-mean-square surface roughness of 2.0 nm. This high-performance GZO material deposited using this approach can pave the way to development of high-conductivity TCOs at low cost from Earth-abundant materials to enable cost-effective solar conversion technologies.