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Description
A single-crystalline ZnGa2O4 epilayer was successfully grown on c-plane (0001) sapphire substrate by MOCVD for application as high performance metal-semiconductor-metal (MSM) visible-blind deep-ultraviolet (DUV) photodetector (PD). The optimized growth parameters for the growth pressure and growth temperature were 15 torr and 650 oC, respectively. The result presented here demonstrate the performance of as grown and annealed at 800 oC in a nitrogen environment for 1 h ZnGa2O4 epitaxial films photodetectors. Compared to as grown ZnGa2O4 film improved UV properties of annealed ZnGa2O4 film were observed. It was found that as-grown films exhibit the highest density of cation-anion pair defects, which could contribute deep trapping centers that increases the generation current or trap assisted leakage current delaying the response and recovery times of as-grown PD devices. However, post-annealing provides sufficient energy to reduce the cation-anion pair defects in the as-grown samples to repair each other. The magnitude of the photocurrent and the rise time are found to increase considerably with decrease number of trap levels. At 5 V bias voltage, the annealed ZnGa2O4 PD shows superior performance with an extremely low dark current of 1 pA, a responsivity of 86.3 A/W corresponding, cutoff wavelength of 280 nm, a highest DUV-to-visible discrimination ratio up to 107 upon 233 nm DUV illumination. The rise time of annealed ZnGa2O4 PD was 0.5 s and PD has been shown a relatively slow decay time of 0.7 s. In this study, our approach provides a simple and controllable method to fabricate single crystalline ZnGaO films based high-performance DUV photodetectors, which has been rarely reported.
