Electronic states of an ordered oxide on C-terminated 6H-SiC

An ordered oxide monolayer with (root 3 x root 3)R30 degrees periodicity wa s obtained on carbon-terminated 6H-SiC(000 (1) over bar) after preparation with a hydrogen microwave plasma. The stoichiometry of this surface was inv estigated by X-ray-induced photoelectron spectroscopy. Most components of t he Si 2p, C Is, and O Is core lines are in agreement with the recently publ ished atomic structure of this ordered monolayer. Beyond this we found hydr ocarbon contamination that could be removed by annealing, and small graphit ized areas remaining on the surface. We used angle-resolved ultra-violet ph otoelectron spectroscopy to examine the electronic structure of the valence band. Besides the O 2s and the O 2p lone pair state at 24 eV and 6 eV resp ectively below the valence band maximum (VBM), we detected a dangling bond state slightly above the VBM and a Si hybrid-O 2p-derived bonding state dis persing between 9.1 and 11.0 eV below the VBM. For the dangling bond state the possibility of a Mott-Hubbard ground state is discussed. In order to cl arify the origin of the oxygen-derived states our results are compared with previous investigations of silicon oxides. (C) 1999 Elsevier Science B.V. All rights reserved.