Si-adatom kinetics in defect mediated growth of multilayer epitaxial graphene films on 6H-SiC

Abstract

We present a quantitative study on the growth of multilayer epitaxial graphene (EG) by solid-state decomposition of SiC on polar (c-plane Si and C-face) and non-polar (a and m planes) 6H-SiC faces, with distinctly different defect profiles. The growth rates are slower than expected from a mechanism that involves Si loss from an open and free surface, and much faster than expected for the nucleation of a defect-free EG layer, implying that defects in the EG play a critical role in determining the growth kinetics. We show that a Deal-Grove growth model, which assumes vertical diffusion of Si through these defects as the limiting factor for EG growth, is unsuitable for describing multilayer growth. Instead, we introduce a lateral “adatom” diffusion mechanism for Si out-diffusion, based on a modified Burton, Cabrera, and Frank model. In this model, defects in epitaxial graphene serve as sinks for Si desorption loss, taking the place of reactive sites, such as step edges for nucleation and growth of crystals produced with external precursors. This analysis shows that the surface diffusion of Si atoms to the grain boundaries of EG limits the growth on c-plane C-face and non-polar faces, rather than the purely vertical diffusion of Si through the grain boundaries described in the Deal-Grove model. However, for Si-face c-plane growth, diffusion of Si to the defects, as well as desorption of Si at the grain boundaries are both relevant, leading to a different temperature trend compared with the other faces. This distinct qualitative difference is ascribed to point-defects in Si-face growth, as contrasted with line defects/grain boundaries on the other faces. The size of the EG grains correlates with the surface diffusion length extracted from this model. The longer a Si adatom diffuses, the higher the quality of the grown EG film, an insight that provides valuable information on Si adatom kinetics for optimizing EG growth. We discuss the applicability of this model to growth of multilayer EG in an argon ambient at atmospheric pressure.