摘要
One of the primary limitations of previously reported two-dimensional (2D) photodetectors is a low frequency response (1 Hz) for sensitive devices with gain. Yet, little efforts have been devoted to improve the temporal response of photodetectors while maintaining high gain and responsivity. Here, we demonstrate a gain of 6.3 × 10 3 electrons per photon and a responsivity of 2.6 × 10 3 A/W while simultaneously exhibiting an ultrafast response time of 40-65 μs in a hybrid photodetector that consists of graphene-WS 2 -graphene junctions covered with indium (In) adatoms atop. The resultant responsivity is 6 orders of magnitude higher than that of conventional photodetectors comprising solely of a Au-WS 2 -Au junction. The photogain is provided mainly by the adsorbed In adatoms, from which photogenerated electrons can be transferred to the WS 2 channel, while holes remain trapped in In adatoms, leading to a photogating effect as electrons are recirculating during the residence of holes in In adatoms. At a gate voltage near the Dirac point of graphene, a detectivity of D∗ = 2.2 × 10 12 Jones and an ON/OFF ratio of 10 4 are achieved. The enhanced performance of the device can be attributed partly to the transparent graphene/WS 2 contact and partly to the strong capacitive coupling of the In adatoms with the WS 2 channel, which enables ultrafast carrier dynamics.