Bias voltage induced n- to p-type transition in epitaxial bilayer graphene on SiC

We show by extensive first-principles calculations that an n- to p-type transition in epitaxial bilayer graphene can be induced by applying bias voltage on C-terminated SiC substrate, but cannot occur on Si-terminated SiC. Bias voltage can cause enough charge transfer between top and bottom graphene layers on C-terminated SiC to shift the Dirac level below or above the Fermi level. On both C- and Si-terminated SiC, change in interlayer spacing of the epitaxial bilayer graphene produces charge redistribution that leads to large increase in the energy gap, but cannot raise the Dirac level efficiently. The surface terminated condition or properties of substrate are of essential importance in possible gate tuning electronic behavior of epitaxial graphene on it.