Photoemission Study on the 6H-SiC(0001) 3×3 Surface

We have investigated the 6H-SiC(0001) √3×√3 R30° and 3×3 surfaces using the valence band spectra and the workfunction change as a function of the Na coverage. The Na-induced ionization energy shift of the √3×√3 R30° surface at the minimum value of the workfunction is in good agreement with the calculated one based on the Si-T4 model in which Na is adsorbed at all DBs. Similar workfunction changes suggest that the 6H-SiC(0001) 3×3 surface has the same density of reactive sites (1/3 ML) as the √3×√3 R30° surface. This result is interpreted in the framework of current models of the 3×3 reconstruction. In particular, we show that the results are not compatible with the accepted Erlangen-Jena model.