k-resolved inverse photoemission of four different 6H-SiC (0001) surfaces -: art. no. 205314

We have investigated the unoccupied electronic states of the Si-terminated (0001) surface of hexagonal 6H-SiC. The main problem with these surfaces is the reliable preparation of well defined surface reconstructions. We give reproducible methods to prepare the (1 X 1), (root3 X root3) R30 degrees, (3 X 3), and the (6 root3 X 6 root3) R30 degrees surface by controlled heating of the SiC sample in a Si flux. These surface reconstructions show a characteristic LEED pattern and a characteristic Si/C peak ratio in Auger electron spectroscopy. We present k-resolved inverse photoemission spectra for the (1 X 1), (root3 X root3) R30 degrees, and (3 X 3) surface. We compare the measured dispersion relations with ab initio local density approximation surface band structure calculations of the (1 X 1)- and the (root3 X root3) R30 degrees -reconstructed 6H-SiC(0001) surface and with a Mott-Hubbard model of the electronic ground state of the (root3 X root3) R30 degrees and (3 X 3) reconstruction. The comparison between experiment and theory supports the Hubbard model: The experiment determines a value of U=2.0 eV for the Mott-Hubbard Coulomb interaction parameter for the (root3 X root3) R30 degrees reconstruction and U=1.25 eV for the (3 X 3)-reconstructed surface, respectively.