Transition of photoresponsivity in graphene–insulator–silicon photodetectors

Abstract

The photocurrent and photoresponsivity of majority-carrier type graphene–insulator–silicon (MC-GIS) photodetectors exhibit a transition from positive to negative as the illuminating optical power decreases below a critical threshold. This transition coincides with a photoinduced alteration of the Schottky barrier height (SBH) relative to its dark state. Interestingly, when the optical power falls below this critical optical power, a notably high negative photoresponsivity (NPR) emerges. This NPR phenomenon is attributed to the photoinduced elevation of the SBH rather than its reduction. For instance, at an optical power of 8.32 nW and a reverse bias voltage of 5 V, the NPRs for red and green LED light illuminations reach approximately −18 600 A W⁻¹ and −14 000 A W⁻¹, respectively. The unusual sign change of photocurrent and photoresponsivity depends on the competition between photoinduced band bending and photoinduced voltage redistribution among graphene, insulator and silicon. This switching mechanism is universally applicable to graphene–insulator–silicon photodetectors and beyond.