  Graphene grown on metal surface, Cu(111), with a boron nitride(BN) buffer
layer is studied for the first time. Our first-principles calculations reveal
that charge is transferred from the copper substrate to graphene through the BN
buffer layer which results in a n-doped graphene in the absence of a gate
voltage. More importantly, a gap of 0.2 eV which is comparable to that of a
typical narrow gap semicondutor opens just 0.5 eV below the Fermi-level at the
Dirac point. The Fermi-level can be easily shifted inside this gap to make
graphene a semiconductor which is crucial for graphene-based electronic
devices. A graphene based p-n junction can be realized with graphene eptaxially
grown on metal surface.
