  We demonstrate hydrogen assisted growth of high quality epitaxial graphene on
the C-face of 4H-SiC. Compared with the conventional thermal decomposition
technique, the size of the growth domain by this method is substantially
increased and the thickness variation is reduced. Based on the morphology of
epitaxial graphene, the role of hydrogen is revealed. It is found that hydrogen
acts as a carbon etchant. It suppresses the defect formation and nucleation of
graphene. It also improves the kinetics of carbon atoms via hydrocarbon
species. These effects lead to increase of the domain size and the structure
quality. The consequent capping effect results in smooth surface morphology and
suppression of multilayer growth. Our method provides a viable route to fine
tune the growth kinetics of epitaxial graphene on SiC.
