Understanding Asymmetric Transportation Behavior in Graphene Field-Effect Transistors Using Scanning Kelvin Probe Microscopy

Scanning Kelvin probe microscopy (SKPM) is applied to experimentally understand the asymmetric behaviors in hole and electron transportation regions in graphene field-effect transistors (FETs). With gate modulation, the transition from p-p-p to p-n-p (for a Ag or Pd source/drain junction with graphene) or from n-p-n to n-n-n (for an Al source/drain junction with graphene) is verified by SKPM, which is believed to be responsible for the asymmetric transport. The odd resistance (R_odd) is positive for Ag (or Pd)/single-layer-graphene (SLG) FETs with ΔWF_intrinsic >; 0, while R_odd is negative for Al/SLG devices with ΔWF_intrinsic <; 0, where ΔWF_intrinsic is defined as the work function difference between metal and intrinsic graphene.