▎ 摘　　要

We measure the channel potential of a graphene transistor using a scanning photocurrent imaging technique. We show that at a certain gate bias, the impact of the metal on the channel potential profile extends into the channel for more than one-third of the total channel length from both source and drain sides; hence, most of the channel is affected by the metal. The potential barrier between the metal-controlled graphene and bulk graphene channel Is also measured at various gate biases. As the gate bias exceeds the Dirac point voltage, V(Dirac), the original p-type graphene channel turns Into a p-n-p channel. When light Is focused on the p-n junctions, an impressive external responsivity of 0.001 A/W is achieved, given that only a single layer of atoms are Involved in photon detection.