▎ 摘　　要

We report the formation of band gaps in as-grown stacks of epitaxial graphene with opposite doping. Control of in-situ doping during carbon source molecular beam epitaxy growth on SiC was achieved by using different carbon sources. Doping heterostructures were grown by stacking n-type material from a C(60) source on p-type material from a graphite filament source. Activation energies for the resistivity and carrier concentration indicated band gaps up to 200 meV. A photoconductivity threshold was observed in the range of the electrical activation energies. Band gap formation is attributed to electric fields induced by spatially separated ionized dopants of opposite charge. (C) 2011 American Institute of Physics. [doi:10.1063/1.3589364]