As-grown Czochralski-type material, with various O contents, was heated to temperatures ranging from 350 to 500C. The O loss during annealing at temperatures of up to 400C was shown to obey second-order kinetics, and measurement indicated values of the O diffusivity which were larger than normal by a factor of about 3; assuming that the capture radius for dimer formation was 0.5nm. Variations in the rate of [Oi] loss during more extended annealing could be explained if the O diffusion was initially enhanced, but tended to its normal value as annealing progressed. A much greater initial enhancement was deduced from similar measurements of samples which had been hydrogenated by heat treatment in H2 gas (1300C, 1.5h), followed by rapid quenching to room temperature. The enhancements were consistent with values which had been deduced from measurements of the relaxation of stress-induced dichroism. At temperatures greater than 450C, the measured rates of [Oi] loss were less than the expected rate of Oi-Oi interaction and tended to vary with increasingly high powers of [Oi]. Modelling of the clustering process demonstrated that the reductions could be explained if the O dimers were present in a quasi-equilibrium concentration throughout annealing. The establishment of this equilibrium appeared to require that O dimers should diffuse much more rapidly than isolated Oi atoms. The kinetics of O loss over the entire range of temperatures could then be explained if dimer clustering led mainly to increases in the concentration of agglomerates which contained large numbers of O atoms (more than 8). It was therefore possible to account for thermal donor formation on the basis of the formation of O clusters of various sizes, although the possibility that self-interstitials were involved in thermal donor formation was not excluded.

S.A.McQuaid, M.J.Binns, C.A.Londos, J.H.Tucker, A.R.Brown, R.C.Newman: Journal of Applied Physics, 1995, 77[4], 1427-42