Ultrahigh deep-UV sensitivity in graphene-gated β-Ga ₂ O ₃ phototransistors

Deep-ultraviolet (UV) photodetectors based on ultrawide bandgap β-Ga ₂ O ₃ have a great potential in civil or military applications especially due to its inherent solar-blindness. Metal-semiconductor phototransistors based on exfoliated β-Ga ₂ O ₃ were fabricated using graphene as a highly transparent gate electrode. Controlling the potential barrier at the metal-semiconductor junction through the UV-transparent graphene gate expanded the difference between the UV-illuminated current and the dark current. Therefore, the photo-to-dark current ratio (PDCR) was raised by 6 orders of magnitude under the optimal gate bias. The performances of β-Ga ₂ O ₃ phototransistors were exceptionally superior among the deep-UV photodetectors based on wide bandgap semiconductor materials; PDCR of 6.0 × 10 ⁸ and rejection ratio of 5.3 × 10 ⁶ could be achieved. The synergetic combination of an ultrawide bandgap semiconductor and two-dimensional UV-transparent graphene provides a new opportunity for high performance deep-UV photodetectors.