A hybrid graphene-PbS quantum dots photodetector with positive and negative photocurrents

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 μA at a low laser power density (0.17 μW), 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 μW), the device exhibits completely opposite characteristics due to thermal scattering. The negative photocurrents of 20 μA 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 graphene-based memristor devices. • We prepared quantum dot modified graphene detectors using graphene grown by LPCVD and PbS quantum dots passiv-ated by EDT. The device exhibits both positive and negative photocurrent under laser irradiation. We explain the negative response mechanism. Then we introduce the gate voltage for modulation and discuss the negative photocurrent response mechanism in detail, and the response principle of devices under high optical power density is derived. At low power density, the device generated positive photocurrents, with a responsivity of 39.58 A/W; while at high power density, negative photocurrents were generated, with a responsivity of 10.29 A/W. This device is helpful to investigate the regulation of graphene carriers, and can also provide a possible research direction for gra-phene-based memristor devices.