Regensburg 2013 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 46: Graphene - SiC Substrates and Intercalation (jointly with DS, HL, MA, and O)
TT 46.5: Vortrag
Mittwoch, 13. März 2013, 17:00–17:15, H17
Graphene on cubic and hexagonal SiC: A comparative theoretical study — Oleg Pankratov, •Stephan Hensel, Paul Götzfried, and Michel Bockstedte — Theoretische Festkörperphysik, FAU Erlangen-Nürnberg, Staudstr. 7B2, D-91058 Erlangen
Epitaxial graphene grows on different SiC polytypes which possess distinct band gaps. We investigate the influence of polytypes on the graphene electronic spectrum employing density functional calculations with LDA and hybrid HSE functionals. We consider different buffer layer-graphene layer stackings as well as different substrate terminations.1 We find a systematic displacement of the Dirac point relative to the valence-band edge as a function of the polytype hexagonality. The HSE values are in good agreement with available experimental results,2,3 while LDA corroborates the trends. The Dirac point, the interface-related states, and the Fermi level follow similar polytype-dependent shifts, hence the graphene doping of the epilayer stays practically the same. For the AB stacked buffer and epilayer on Si-terminated SiC the Dirac spectrum exhibits an energy gap of 25-40 meV (depending on the polytype). On the contrary, for the AA stacking the Dirac cone remains intact. We suggest a symmetry-based analytical model which explains the origin of the gap and its absence for the AA geometry.
[1] Pankratov et al. Phys. Rev. B 86, 155432 (2012).
[2] Sonde et al., Phys. Rev. B 80, 241406 (2009).
[3] Ristein et al., Phys. Rev. Lett. 108, 246104 (2012).