Effect of deposition distance and temperature on electrical, optical and structural properties of radio-frequency magnetron-sputtered gallium-doped zinc oxide

Films of gallium-doped zinc oxide (GZO) were deposited on glass substrates by radio-frequency magnetron sputtering using a ceramic target of Ga:ZnO (4 at.% Ga vs. Zn). Both the substrate temperature (Ts) and the target-substrate distance (dts) were varied and the effect on electrical, optical and structural properties of the resulting films were measured. The highest conductivity of 3200 S/cm was obtained at a deposition temperature of 250 °C, at a dts of 51 mm. This sample had the highest carrier concentration in this study, 9.6 × 1020/cm3. Optical transmittance of all films was <90% in the visible range. The grain size of the film grown at dts = 51 mm was smaller than the grain size for films grown with a shorter dts; moreover, the films with dts = 51 mm exhibited the smoothest surface, with a root mean square surface roughness of 2.7 nm. Changes in Ts have a more pronounced effect on conductivity compared to changes in dts; however, variations in structure do not appear to be well-correlated with conductivity for samples in the 2000-3200 S/cm range. These results suggest that incorporation and activation of Ga is of key importance when attempting to obtain GZO films with conductivities greater than 2000 S/cm.