Engineering the electronic structure of epitaxial graphene by transfer doping and atomic intercalation

Homogeneous graphene layers can be grown epitaxially on SiC(0001), promising scalable graphene technology. However, covalent bonds at the SiC-graphene interface induce strong n-doping of the graphene. This doping can be compensated by functionalizing the graphene surface with electronegative molecules. Alternatively, the influence of the substrate can be largely suppressed by breaking the covalent bonds through atomic intercalation. Hydrogen atoms migrate under the graphene, passivate the underlying SiC layer, and decouple the graphene from the substrate. In this way, large-scale, homogeneous, quasi-free-standing graphene layers can be achieved. By intercalation of germanium, the electronic structure of the decoupled graphene can be tailored. Two symmetrically doped, namely, n- and p-type, phases are stabilized, depending on the amount of intercalated germanium. This is achieved by annealing a germanium film at various temperatures after it is initially deposited on the covalently bonded carbon layer. In an intermediate temperature regime, lateral p-n junctions between the two phases can be formed, size-tailored on a mesoscopic scale.