THE (√3 x √3)R30°-reconstructed 6H-SiC(0001):: A semiconducting surface

k(//)-resolved inverse-photoemission spectroscopy of the (root 3 x root 3)R30 degrees reconstruction of 6H-SiC(0001) reveals a sharp surface state U located 1.10 +/- 0.05 eV above the Fermi level at the center of the surface Brillouin zone with a total bandwidth of 0.34 +/- 0.05 eV. This value is in good agreement with recent LDA calculations which predict an adatom-induced surface state Sigma(1) which should be half-filled. In this model, the adatoms are Si atoms occupying the T-4 Site above a compact SiC(0001) (Si) termination. In contrast to the predicted metallic behavior, the U state remains completely unoccupied throughout the whole Brillouin zone, and the surface is semiconducting. We propose that some charge transfer from the Si adatoms towards subsituted C atoms in the terminating bilayer stabilizes the reconstruction by moving up the Sigma(1) state away from the Fermi level.