Deep-ultraviolet Schottky photodetectors with high deep-ultraviolet/visible rejection based on a ZnGa₂O₄ thin film

A single-crystalline ZnGa₂O₄ epilayer was successfully grown on a c-plane (0001) sapphire substrate through metalorganic chemical vapor deposition. A metal-semiconductor-metal Schottky deep-ultraviolet (DUV) photodetector based on a ZnGa₂O₄ thin film was fabricated through a simple process of E-gun evaporation and thermal annealing. At a bias of 10 V, the ZnGa₂O₄ photodetectors exhibited excellent performance characteristics such as an extremely low dark current (0.86 pA), a responsivity of 0.46 A/W under 230-nm DUV, a high photo/dark current ratio (up to 4.68 × 10⁴), a sharp cutoff wavelength of approximately 270 nm, and short rise and fall times of 0.96 and 0.34 s. The photogenerated holes trapped in the Schottky barrier and the shrinking of the depletion region under DUV illumination enabled high DUV/visible rejection ratio (3–4 orders with a 20-V bias). Therefore, the Fowler–Nordheim field tunneling emission functioned as the main electron transport mechanism under DUV illumination and improved the photoelectric characteristics of the epilayer.