Dopant induced electronic inhomogeneity of epitaxial bilayer graphene in SiC*

Graphene has been a promising candidate for next-generation electronics due to its intriguing properties, particularly the high carrier mobility. Currently, wafer-scale single crystal graphene could be readily produced on silicon carbide (SiC) substrate by high-temperature annealing. But the mobility of epitaxial graphene is relatively lower than that by mechanical exfoliation. The underlying mechanism has not yet been resolved. Here we study the topography and electronic state of epitaxial graphene grown on 6H-SiC by scanning tunneling microscopy (STM) and spectroscopy (STS). We show that the nitrogen dopants inside SiC substrate result in the electronic inhomogeneity of epitaxial graphene, and give rise to electron-lack puddles. Our results provide the plausible microscopic mechanism for the low mobility in epitaxial graphene.