Fast gate-tunable photodetection in the graphene sandwiched WSe₂/GaSe heterojunctions

We investigated electrical and photoelectrical properties of graphene sandwiched WSe₂/GaSe van der Waals heterojunctions. The device showed a high rectification ratio up to 300 at V_ds = 1.5/-1.5 V, which is attributed to the built-in electric field in the device. Due to the bipolar property of WSe₂, gate-tunable rectification inversion was observed. Meanwhile, the graphene sandwiched heterojunction showed excellent performances on photodetection, where the photoresponsivity of (6.2 ± 0.2) A W^-1 can be reached under V_ds = -1.5 V and P = 0.2 μW. The device also showed great external quantum efficiency of (1490 ± 50)% and fast response time of ∼30 μs. Our study identified the graphene sandwiched heterojunctions based on 2D materials have great potential for gate-tunable electronic and optoelectronic applications.