Ambipolar behavior in epitaxial graphene-based field-effect transistors on Si substrate

In this research, ambipolar behavior, which is one of graphene's unique characteristics, is studied for the epitaxial graphene formed on 3C-SiC grown on a Si substrate. The graphene channel is believed to be unintentionally p-type-doped at Dirac-point voltages of approximately +0.11 to +0.12 V. However, as drain voltage negatively increases, Dirac point voltage shifts. The drain current in the p-channel mode of operation saturates at a lower level than that in the n-channel mode of operation. These behaviors are caused by asymmetric carrier transport throughout channelsubstrate heterojunctions (i.e., graphene, thin n-type SiC layer, and p-type Si substrate) and source/drain Schottky metal contacts. The interface between the p-type Si substrate and n-type SiC has a significant effect on transport in graphene channels. The results may be helpful for understanding transport in the device and for suppressing ambipolar operation, leading to a unipolar FET operation.