Electronic properties of the graphene/6H-SiC(000(1)over-bar) interface: A first-principles study

Using calculations from first principles, we show how the structural and electronic properties of epitaxial graphene on 6H-SiC(000 (1) over bar) are determined by the geometry and the chemical functionalization of the interface region. We also demonstrate that these properties can be correctly captured only if a proper treatment of the van der Waals interactions is included in the theoretical description based on density functional theory. Our results reproduce the experimentally observed n-type doping of monolayer epitaxial graphene and prove the possibility of opening a sizable (150 meV) energy gap in the bilayer case under special growth conditions. Depending on the details of the bonding at the interface, we are able to interpret recent experimental observations and provide a clear insight into the mechanisms of charge transfer and interface stability.