Electron correlation effects on SiC(111) and SiC(0001) surfaces

The possibility is discussed that, independent of the polytype, large electronic correlation effects give rise to semiconducting SiC surfaces with [111] or [0001] orientations. The most important surface translational symmetries (\sqrt {3}\times \sqrt {3}){\mathrm

{R}}30^\circ and 3 × 3 are considered. The discussion is based on the detailed knowledge of the surface atomic geometries and the electronic structures derived for these geometries using a local density approximation for exchange and correlation. It is argued that the resulting half-filled, weakly dispersive dangling-bond bands within the fundamental gaps are split according to a Hubbard interaction parameter U, and that the surface systems undergo a Mott-Hubbard transition. Such a physical picture provides a qualitatively correct account of the single-particle excitation spectra either inferred from angle-resolved photoemission and inverse photoemission experiments or obtained from scanning tunnelling spectroscopy. The gap opening and hence the Hubbard U parameter are discussed in terms of their dependence on the surface reconstruction as well as the SiC polytype.