Solid-state graphitization mechanisms of silicon carbide 6H-SiC polar faces

Due to the higher vapour pressure of silicon, silicon carbide surfaces annealed at high temperature under vacuum tend to graphitize. The comparison of graphite formation on the silicon and carbon terminations of 6H-SiC reveals significant differences in the graphitization mechanisms involved. The conduction-band structure of these interfaces has been determined by angle-resolved inverse photoemission spectroscopy (KRIPES). Although the graphite layers grown on the C face are essentially polycrystalline, a small fraction of the film keeps a preferred orientation, where the graphite lattice basis vectors are rotated by 30 degrees with respect to the basis vectors of the SiC lattice as in the case of the Si face. This in-plane disorder is in contrast with the growth of graphite on the Si face that takes place on a "passivated" adatom-terminated surface, leading to single-crystalline, heteroepitaxial graphite growth. The observation of unshifted pi* states indicates a very small interaction of the first graphite monolayer with the Si face. In contrast, KRIPES reveals that the first graphite layer is strongly bound to the C face. A rehybridization of the graphite pi* states with occupied orbitals of the substrate: is inferred from an observed increase in the density of states in the vicinity of the Fermi level. (C) 2000 Elsevier Science B.V. All rights reserved.