Unoccupied surface state on the (√3 × √3) R30° of 6H-SiC(0001)

Applying k-resolved inverse photoemission (KRIPES) to the $\sqrt 3\times \sqrt3$ $\rm R30^\circ$-reconstructed 6H-SiC(0001) face, we have observed a sharp surface state U located at $1.10 \pm 0.05\;{\rm eV}$ above the Fermi level at the centre of the surface Brillouin zone. Its bandwidth of $0.34 \pm 0.05\;{\rm eV}$ is in good agreement with the 0.35 eV predicted by first-principle calculations based on a Si-adatom model. However, LDA calculations predict a half-filled ${\mit\Sigma}_1$ state and a metallic character for this reconstruction. Together with recent ARUPS data, our results reveal that the one-electron band ${\mit\Sigma}_1$ is split into two bands, giving a semiconducting surface with a reduced indirect bandgap around 2.0 eV at the $\bar K'$ point. Many-body correlation effects may give rise, in the limit of strong localization, to this bandgap opening.