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 (T_s) and the target-substrate distance (d_ts) 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 d_ts of 51 mm. This sample had the highest carrier concentration in this study, 9.6 × 10²⁰/cm ³. Optical transmittance of all films was <90% in the visible range. The grain size of the film grown at d_ts = 51 mm was smaller than the grain size for films grown with a shorter d_ts; moreover, the films with d_ts = 51 mm exhibited the smoothest surface, with a root mean square surface roughness of 2.7 nm. Changes in T_s have a more pronounced effect on conductivity compared to changes in d_ts; 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.