WS/Graphene/MoS Sandwich van der Waals Heterojunction for Fast-Response Photodetectors.

Fast-response photodetectors have attracted considerable attention in the application of high-speed communication, real-time monitoring, and optical imaging systems. However, most reported photodetectors suffer from limitations of the inherent properties of materials, low carrier transport efficiency, and unmatched interfaces, which lead to a low response speed. Here, we report a WS/graphene/MoS vertical van der Waals heterojunction fabricated by mechanical exfoliation and dry transfer methods for fast response. To improve the response speed of the previously reported WS/MoS heterojunction with excellent photoelectric performances, the embedded graphene is employed to optimize the interface defects and improve the carrier transport efficiency due to its high mobility and smooth and flat surface. Under the illuminations of a 405 nm laser and a bias voltage of 0.5 V, our device can realize rise and fall times of 44 and 52 μs, respectively. For a bias voltage of 2.5 V, moreover, the device can also show outstanding performances including a high responsivity of 220 A/W, a considerable detectivity of 1.2 × 10 Jones, a large external quantum efficiency of 6.7 × 10 %, and a low dark current of 1.05 × 10 A. Additionally, the device enables high-speed transmission with a low bit error rate in a closed-loop optical communication system. Therefore, the proposed scheme can provide an idea for the design of photodetectors with fast response and high performance.