Bonding Arrangements at the $\mathrm{Si}-{\mathrm{SiO}}_2$ and $\mathrm{SiC}-{\mathrm{SiO}}_2$ Interfaces and a Possible Origin of their Contrasting Properties

We report ab initio calculations designed to explore the relative energetics of different interface bonding structures. We find that, for Si (001), abrupt (no suboxide layer) interfaces generally have lower energy because of the surface geometry and the softness of the Si-O-Si angle. However, two energetically degenerate phases are possible at the nominal interface layer, so that a mix of the two is the likely source of the observed suboxide and dangling bonds. In principle, these effects may be avoidable by low-temperature deposition. In contrast, the topology and geometry of SiC surfaces is not suitable for abrupt interfaces.