Electronic properties of epitaxial graphene residing on SiC facets probed by conductive atomic force microscopy

In this paper, the electronic transport in few layer graphene epitaxially grown on the Si face of 8° off-axis 4H-SiC has been investigated using conductive atomic force microscopy (CAFM). The comparison between the two dimensional morphology and current maps in epitaxial graphene (EG) residing over the stepped SiC surface revealed a local resistance increase of EG over the (11 − 2n) facets with respect to the (0 0 0 1) basal plane. This is consistent with a significant reduction of the carrier concentration, possibly approaching to the neutrality, in EG residing on facets with respect to the high n-type doping (∼1013 cm−2) commonly found in EG on the basal plane. The observed difference can be ascribed to a different interface structure between EG and SiC on the two faces. The results of these nanoscale measurements allow us to explain the typically observed macroscopic anisotropy in EG conductivity with respect to the substrate steps orientation.