Paper GR+SS-MoA6
Formation of Epitaxial Graphene on SiC{0001}: Comparison of Si-face and C-face
Monday, November 9, 2009, 3:40 pm, Room C3
Session: |
Epitaxial Graphene on SiC |
Presenter: |
P. Fisher, IBM |
Authors: |
P. Fisher, IBM L. Luxmi, Carnegie Mellon University N. Srivastava, Carnegie Mellon University R. Feenstra, Carnegie Mellon University Y. Sun, Argonne National Laboratory J. Kedzierski, MIT Lincoln Laboratory |
Correspondent: |
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The formation of epitaxial graphene on the SiC{0001} surface is described, comparing results for (0001) and () surfaces (the so-called Si-face and C-face, respectively). The graphene is formed by heating the SiC to 1100 – 1400°C for 20 min in vacuum, during which time the Si preferentially sublimates, leaving behind the C which self-assembles into graphene. Development of the graphene layer(s) is observed by atomic force microscopy (AFM), low-energy electron diffraction and Raman spectroscopy, with the graphene thickness measured using both Auger electron spectroscopy and low-energy electron microscopy. High quality films are formed, with field-effect mobilities at room temperature exceeding 4000 cm2/Vs. It is found that graphene forms as 3-dimensional islands on the C-face, whereas it forms in a 2-dimensional manner on the Si-face. We believe that this difference occurs because of differing interface structures between the graphene and the SiC in the two cases. Importantly, the graphene for the C-face is found to be thinner in the areas on top of the islands, consistent with a model in which sublimating Si atoms originate from the interface (and hence thicker graphene implies more material loss). For the Si-face a number of morphological features are found to interrupt the flat, uniform morphology of the graphene, including: surface pits, step bunches, and an apparent "secondary" graphitic surface phase. This secondary phase is observed as locally rough regions in the surface morphology. At low graphene formation temperature these regions can extend substantially over the entire surface, but at higher formation temperatures the regions shrink in size, until they produce only a faint finger-like pattern in the morphology as seen by AFM. We tentatively interpret the secondary phase as arising from excess carbon present on top of the surface (as opposed to at the graphene/SiC interface, where it would form well-ordered graphene).