Unveiling the Hot Carrier Distribution In Vertical Graphene/h-BN/Au Van der Waals Heterostructures for High Performance Photodetector.

Graphene is one of the most promising materials for photodetectors due to its ability to convert photons into hot carriers within approximately 50 fs and generate long-lived thermalized states with lifetimes longer than 1 ps. In this study, we demonstrate a wide-range vertical photodetector comprising a graphene/h-BN/Au heterostructure in which a h-BN insulating layer is inserted between an Au electrode and graphene photo absorber. The photocarriers effectively tunnel through the small hole barrier (1.93 eV) at the Au/h-BN junction while the dark carriers are highly suppressed by a large electron barrier (2.27 eV) at the graphene/h-BN junction. Thus, an extremely low dark current of ~10-13 A is achieved, which is 8 orders of magnitude lower than graphene lateral photodetector devices (~10-5 A). Also, our device displays an asymmetric photo-response behavior due to photo-thermionic emission at the graphene/h-BN and Au/h-BN junctions. The asymmetric behavior generates additional thermal carriers (hot carriers) to enables our device to generate photocurrents that can overcome the Schottky barrier. Furthermore, our device shows the highest value of Iph/Idark ratio ~225 at 7 nm-thick of h-BN insulating, which has 3 orders of magnitude larger than in previous reported graphene lateral photodetectors without any active materials. In addition, we achieve a fast response speed of 12 μs of rise time and 5 μs of fall time about 100 times faster than other graphene integrated photodetectors.