摘要
We investigate the initial oxidation of the Si-rich (formula presented) 3×3 and (formula presented) 3×3 surfaces and the subsequent (formula presented) and (formula presented) initial interface formation by Si 2p, C 1s, and O 1s core-level photoemission spectroscopy using synchrotron radiation. The 3×3 surface reconstruction is found to be highly reactive to oxygen with an initial oxidation rate of about three to four orders of magnitude larger than for silicon surfaces. Furthermore, for both polytypes, direct (formula presented) interface formation is achieved already at room temperature and extremely low oxygen exposures. However, the two polytypes have significantly different behaviors with larger amounts of oxide products having higher oxidation states for the (formula presented) 3×3 surface, while mixed oxides including carbon species (Si-O-C) are the dominant oxide products for the 4H polytype surface. The oxidation rate is improved at increased surface temperatures. In all cases, the oxygen uptake remains significantly larger for the 6H polytype when compared to the 4H one. The very different behavior of the 6H and 4H polytypes seems to originate, at least in part, from the presence of two domains in the bulk for the 4H polytype (as evidenced by two bulk components in the Si 2p core-level spectrum) which limits the oxygen insertion into the (formula presented) lattice. Instead the 6H polytype has only one bulk domain with a single Si 2p bulk component. Abrupt (formula presented) interfaces could be achieved by thermal oxidation of a predeposited Si overlayer onto the surface leading to have oxide thicknesses ranging from 10 Å up to 80 Å after postoxidation with a transition layer of less than 5 Å. This study shows that, using a “gentle” initial oxidation approach at low temperatures and low oxygen exposures allow high-quality (formula presented) interfaces. It also brings interesting insights into the understanding of polytype crucial effect in SiC surface oxidation. © 2002 The American Physical Society.