  Controlling the type and density of charge carriers by doping is the key step
for developing graphene electronics. However, direct doping of graphene is
rather a challenge. Based on first-principles calculations, a concept of
overcoming doping difficulty in graphene via substrate is reported.We find that
doping could be strongly enhanced in epitaxial graphene grown on silicon
carbide substrate. Compared to free-standing graphene, the formation energies
of the dopants can decrease by as much as 8 eV. The type and density of the
charge carriers of epitaxial graphene layer can be effectively manipulated by
suitable dopants and surface passivation. More importantly, contrasting to the
direct doping of graphene, the charge carriers in epitaxial graphene layer are
weakly scattered by dopants due to the spatial separation between dopants and
the conducting channel. Finally, we show that a similar idea can also be used
to control magnetic properties, for example, induce a half-metallic state in
the epitaxial graphene without magnetic impurity doping.
