Role of atomic terraces and steps in the electron transport properties of epitaxial graphene grown on SiC

Thermal decomposition of vicinal SiC substrates with self-organized periodic nanofacets is a promising method to produce large graphene sheets toward the commercial exploitation of graphene's superior electronic properties. The epitaxial graphene films grown on vicinal SiC comprise two distinct regions of terrace and step; and typically exhibit anisotropic electron transport behavior, although limited areas in the graphene film showed ballistic transport. To evaluate the role of terraces and steps in electron transport properties, we compared graphene samples with terrace and step regions grown on 4H-SiC(0001). Arrays of field effect transistors were fabricated on comparable graphene samples with their channels parallel or perpendicular to the nanofacets to identify the source of measured reduced mobility. Minimum conductivity and electron mobility increased with the larger proportional terrace region area; therefore, the terrace region has superior transport properties to step regions. The measured electron mobility in the terrace region, ∼1000 cm2/Vs, is 10 times larger than that in the step region, ∼100 cm2/Vs. We conclusively determine that parasitic effects originate in regions of graphene that grow over step edges in 4H-SiC(0001).