First-principles calculations in the local-density approximation were carried out on SiC in order to determine the possible configurations of the isolated O impurity. Equilibrium geometries and occupation levels were calculated. Substitutional O in 3C-SiC was a relatively shallow effective mass, like the double donor on the C site (OC) and the hyper-deep double donor on the Si site (OSi). In 4H-SiC, OC was still a double-donor; but with a more localized electron state. In 3C-SiC, OC was substantially more stable under any conditions than were OSi or interstitial O (Oi). In 4H-SiC, OC was also the most stable one; except for heavy n-type doping. It was proposed that OC was at the core of the electrically active O-related defect family detected by deep-level transient spectroscopy in 4H-SiC.

Isolated Oxygen Defects in 3C- and 4H-SiC - a Theoretical Study. A.Gali, D.Heringer, P.Deák, Z.Hajnal, T.Frauenheim, R.P.Devaty, W.J.Choyke: Physical Review B, 2002, 66[12], 125208 (7pp)