Intrinsic Origin of Negative Fixed Charge in Wet Oxidation for Silicon   Carbide
  We demonstrate on the basis of first-principles calculations that the formation of carbonate-like moiety in SiO$_2$ could be the intrinsic origin of negative fixed charge in SiC thermal oxidation. We find that two possible origins for the negative fixed charges are O-lone-pair state and a negatively charged CO$_3$ ion in SiO$_2$. Such CO$_3$ ion is able to be formed as a result of the existence of residual C atoms in SiO$_2$, which are expected to be emitted from the interface between SiC and SiO$_2$, and the incorporation of H atoms during wet oxidation. 
Yasuhiro Ebihara, Kenta Chokawa, Shigenori Kato, Katsumasa Kamiya,   Kenji Shiraishi
cond-mat.mtrl-sci