Unoccupied Mott-Hubbard State On The (Root 3 X Root 3)R30 Degrees Reconstructed 4h-Sic(0001) Surface

We have investigated the (root3xroot3)R30degrees reconstructed 4H-SiC(0001) surface using (k) over right arrow -resolved inverse photoemission. Undergoing a Mott-Hubbard transition a formerly half-filled surface band splits into a completely occupied and a completely unoccupied band. We observe a sharp peak at an energy of 1.10 eV above the Fermi level. By mapping the dispersion E((k) over right arrow) of this surface state we show that it remains above the Fermi level throughout the whole surface Brillouin zone, thus confirming the semiconducting character of the surface. As expected for a strongly correlated system the dispersion is flat with a determined bandwidth of W = (0.26 +/- 0.10) eV. Including recent ARUPS measurements we are able to deduce a Mott-Hubbard parameter of U = (2.2 - 0.2) eV. These results are in accordance with experiments performed on the 6H-SiC(0001) surface, which shows a slightly different electronic structure. We therefore confirm that the Mott-Hubbard splitting for the (root3xroot3)R30degrees reconstructed surface is independent of the underlying polytype as predicted by theory.