An ab initio method was used to study intrinsic interstitials, vacancy-antisite complexes, B interstitials and B-vacancy complexes. The electronic and atomic structures, as well as the defect energetics, were calculated and the stability of substitutional B and the migration of impurities were considered. It was noted that the physics of intrinsic, as well as B-related defects, were distinctly different in SiC as compared with Si. The most striking difference was that on-site B was metastable, due to interactions with intrinsic interstitials and vacancies. The resultant B interstitials and B-vacancy complexes were deep centres. This process was expected to diminish the doping efficiency. The successful preparation of electrically active B-doped 4H-polytype samples suggested that these reactions were kinetically suppressed; partly due to the large migration barriers of the intrinsic defects and partly because of the formation of more stable intrinsic defect complexes. In p-type or intrinsic specimens, Si interstitials and C vacancies were the most abundant mobile intrinsic point defects. The equilibrium concentrations of both defects were comparable under these conditions. Under n-type conditions, the C vacancy was more abundant because it had a lower formation energy. A lower bound on the migration barrier for Si interstitials was deduced to be equal to 4eV, in p-type material, by assuming that it occurred between SiTC sites; with other stable sites as intermediate stages. A nearest-neighbour mechanism for the diffusion of C vacancies was eliminated because the vacancy-antisite complex which formed during the first stage of such a mechanism was unstable.

Ab initio Study of Intrinsic Point Defects and Dopant-Defect Complexes in SiC - Application to Boron Diffusion. M.Bockstedte, O.Pankratov: Materials Science Forum, 2000, 338-342, 949-52