Ab initio study of the relationship between spontaneous polarization and p-type doping in quasi-freestanding graphene on H-passivated SiC surfaces

摘要

The recent proposal of a direct equivalence between the p-type doping typically found in quasi-free-standing graphene (QFG) obtained on H-passivated silicon carbide surface and the spontaneous polarization (SP) associated to the particular SiC polytype, opens the possibility of tuning the number of carriers in the Dirac cones without the need of external gate voltages. However, first-principles calculations which could confirm at the atomic scale the effect of the SP are lacking mainly due to the difficulty of combining a bulk property such as the SP with the surface confined graphene doping. Here we develop an approach based on standard density functional theory (DFT) calculations in order to quantify the effect of the SP on the QFG's doping level. To this end, a double gold layer is attached at the C-terminated bottom of the slab which introduces a metal-induced gap state that pins the chemical potential inside the gap thus allowing a meaningful comparison of the QFG's dopings among different polytypes. Our model is generalized by performing large-scale DFT calculations where self-doping in the QFG is included via point defects in order to estimate the interplay between both sources of p-type doping (SP-versus defectinduced) which turns out to be essentially additive. (C) 2015 Elsevier Ltd. All rights reserved.