A Study of Different Annealing Ambiences on the Performance of ZnGa₂O₄ UVC Photodetectors by Ultrasonic Spray Pyrolysis Deposition

This study presents ZnGa2O4 thin films, which are prepared on c-plane sapphire by ultrasonic spray pyrolysis deposition (USPD) and postdeposition annealing techniques. The postannealing process was carried out at a temperature of $800~^{\circ }$ C in various ambiences, such as oxygen, nitrogen, and air. A systematic analysis was conducted on the material properties, such as crystalline quality and optical performance of ZnGa2O4 thin films after annealing. The material analyses indicate that the crystallinity, surface roughness, oxygen vacancy, and energy bandgap of the ZnGa2O4 were significantly improved through annealing. The ZnGa2O4 photodetector annealed at air shows the largest photo/dark current ratio of $\sim 10^{{6}}$ and a high maximum responsivity of 24.7 A/W at a wavelength of 240 nm and bias of 5 V. These results suggest the potential of spinel ZnGa2O4 thin films in the applications of UVC detection.