Photo-induced charge flow of graphe-based field effect device

 Graphene-based field effect transistor(GFET) exhibits a large photo-induced current change. This effect is utilized for photo detector applications.  However the underlying mechanism for the current change is not solidly established. Here we fabricated GOS(graphene/oxide/p-Si) field effect device and measured I_DS and I_GS currents while manipulating the light. Upon turning on the light, a short-lived current I_GS flow is observed in concurrence with permanent I_DS jump. 

We find that two charge densities associated with Isd and Isg are in agreement with each other, providing direct evidence for the hole migration from Si to G and establishing a photo-gating mechanism of GFET.  We further show that I_DS-jump can be enhanced as the gate bias Vg is increased which enables the use of GFET for weak-intensity photo detection.