Voltage-tunable graphene/β-Ga ₂ O ₃ heterojunction solar-blind photodetector enabling photovoltaic and photoconductive dual-mode operation

Solar-blind ultraviolet photodetectors based on β-Ga 2 O 3 are attractive for both military and civilian applications, yet photoconductors suffer from slow response and photovoltaic photodiodes suffer from limited responsivity. Herein, we report a voltage-tunable graphene/β-Ga 2 O 3 heterojunction photodetector with dual-mode operation. Under reverse bias, it functions as a photodiode with 150 mA/W responsivity, 71% external quantum efficiency (EQE), and 0.5 ms response time at 254 nm. Forward bias switches it to photoconductive mode, achieving 71 A/W responsivity and EQE above 35,000% with 60 ms response time. This bias-selectable behavior integrates high-speed and high-gain operation in one device, enabling advanced communication and imaging applications.