LAUSR

van der Waals heterostructures built from two-dimensional (2D) materials have attracted wide attention because of their fascinating electrical and optoelectronic properties. Here, we report a highly responsive and broadband photodetector based on WS2–graphene van der Waals epitaxial heterostructures, which were fabricated by directly growing single crystalline few layer WS2 nanosheets on a polycrystalline graphene film. Upon light illumination, the current apparently reduces because of the transfer of photogenerated electrons from WS2 into the underlying p-type graphene and a photo-gating effect induced by the remaining holes, which is in stark contrast to ordinary semiconducting photoconductors. Thanks to the strong and broadband absorption of WS2, the WS2–graphene heterostructure photodetector exhibits a high responsivity with a maximum of 950 A W−1 at 405 nm and a wide spectrum response ranging from 340 to 680 nm. The high performance can be attributed to the internal built-in electric field at the WS2–graphene interface, which leads to the efficient separation of photogenerated electron–hole pairs. The WS2–graphene heterostructure photodetector may have potential applications in low cost, broadband, and flexible optoelectronics.