Optical and electrical characterization of transparent conductive Gd-doped AZO thin films

The Gd-doped Al-doped Zn oxide (AZO) thin films are prepared and characterized in this study. The findings show that when the Gd doping concentration exceeded a threshold of approximately 3-5 wt%, the resistivity of the Gd:AZO thin film was reduced to a point that was lower than the resistivity of the pure AZO thin film. The reduction in resistivity was caused by the increase of the carrier concentration. This study proposes that the increase in carrier concentration was caused by the additional Gd³⁺-Zn ²⁺ substitution reaction. After performing 10 wt% Gd doping, the transmittance of the Gd:AZO thin film in the near UV region was increased. Following an annealing process at 200 °C, the transmittance of the annealed 100-nm Gd:AZO (10 wt%) thin films was over 80% at the 375 nm wavelength, which was approximately 40% higher than that of the annealed pure AZO thin film. The 600-nm Gd:AZO (10 wt%) annealed at 200 °C is found to have the best figure of merit value (0.24 ohm^-1) at 375 nm (near UV regime) among all studied Gd:AZO (10 wt%) thin films in this study.