Ultra-wide bandgap zinc gallium oxide (ZGO) and GO films were prepared on c-plane sapphire by conventional radio-frequency magnetron sputtering. In the current sputtered oxide studies, target composition or growth temperature is usually the main deposition variable, and the other growth conditions are fixed. This would make it difficult to fully understand the theory and characterization of ZGO films. In this study, several growth parameters as well as the post-thermal treatment were all modulated to realize and optimize the ZGO growth. From x-ray and TEM analyses, stabilization of stoichiometry and control of crystallinity transformation were confirmed to be important factors in determining the film quality. The optical bandgap of ZGO can reach 5.0-5.1 eV with a maximum responsivity peak at 240 nm. A metal-semiconductor-metal photodetector is demonstrated with a maximum responsivity over 2 A/W under a 5-V biased voltage. Furthermore, the photo/dark current ratio can be improved to be over ten thousand. As compared with those of the sputtered GO photodetector, the spectral response peak of ZGO showed a blue shift to 240 nm with higher responsivity. The data presented exhibit the ZGO material will become another potential candidate for ultra-wide bandgap semiconductor applications.
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