Lateral uniformity of the transport properties of graphene/4H-SiC (0001) interface by nanoscale current measurements

Conductive Atomic Force Microscopy was applied to study the lateral uniformity of current transport at the interface between graphene and 4H-SiC, both in the case of epitaxial graphene (EG) grown on the Si face of 4H-SiC and in the case of graphene exfoliated from HOPG and deposited (DG) on the same substrate. This comparison is aimed to investigate the role played by the C-rich buffer layer present at EG/4H-SiC interface and absent in the case of DG/4H-SiC. The distribution of the local Schottky barrier heights at EG/4H-SiC interface (? EG) was compared with the distribution measured at DG/4H-SiC interface (? DG), showing that ? EG (0.36±0.1eV) is ~0.49eV lower than ? DG (0.85 ± 0.06eV). This difference is explained in terms of the Fermi level pinning ~0.49eV above the Dirac point in EG, due to the presence of positively charged states at the interface between the Si face of 4H-SiC and the buffer layer.