Temperature-dependence of Epitaxial Graphene Formation on SiC(0001)

The formation of epitaxial graphene on SiC(0001) (the \textit{Si-face}) is studied using atomic force microscopy, Auger electron spectroscopy, low energy electron diffraction/microscopy, Raman spectroscopy, and electrical measurements. Starting from hydrogen-etched surfaces, graphene formation by vacuum annealing is observed to begin at about 1150\r{ }C, with the overall step-terrace arrangement of the H-etched surface being preserved but with significant roughness (pit formation) on the terraces. At temperatures near 1350\r{ }C, the surface morphology changes into relatively large flat terraces covered with several layers of graphene and containing a few large pits, with the terraces separated by step bunches. On the terraces the graphene thickness varies by typically $\pm $1 monolayer. At higher temperatures the graphene film is observed to buckle and break up, presumably due to thermal mismatch with the SiC. Field-effect mobilities as high as 4200 cm$^{2}$/Vs for few-layer graphene films are found.