▎ 摘　　要

Different graphene photodetectors may have different light response mechanisms, and in general, most graphene photodetectors tend to generate only positive or negative photocurrents. Here, we demonstrate a photodetector based on graphene grown by Chemical Vapor Deposition (CVD) and PbS quantum dots (QDs) with both positive and negative photocurrents. Under the irradiation of a 635 nm laser, the device generated positive photocurrents of 9 mu A at a low laser power density (0.17 mu W), the responsivity of which was up to 39.58 A/W due to the high gain mechanism. However, at high laser power density (9.59 mu W), the device exhibits completely opposite characteristics due to thermal scattering. The negative photocurrents of 20 mu A were generated and the responsivity of the device was 10.29 A/W. The device exhibits the coexistence of two response mechanisms. It is necessary to explore the mechanism of positive and negative photocurrent in graphene, which is helpful to investigate the regulation of graphene carriers, and can also provide a possible research direction for graphenebased memristor devices.