Enhanced photoresponse in interfacial gated graphene phototransistor with ultrathin Al₂O₃ Dielectric

An interfacial-gated graphene phototransistor sensitized by silicon substrate with an ultrathin 3-nm Al₂O₃ dielectric layer is demonstrated. When applying gate voltages larger than a certain threshold, the phototransistor exhibits a photo-induced switching-on behavior, giving rise to its capacity of detecting light with the ultralow power of 470 pW, with a high responsivity of 1.4 × 10⁴ A/W. The temporal measurements unveil a fast photoresponse speed with a rising time of 2μs. The novel channel on-state trigged by light was not observed in a control device with 16-nm Al₂O₃. The difference of transfer characteristics in the dark and under illumination is assigned mainly to the photo-assisted modification of the silicon depletion region.