Czochralski-type samples which contained a range of grown-in O concentrations were annealed at temperatures of up to 500C, and the rates of Oi loss due to solution and thermal donor formation were monitored. The results could be explained in terms of serial O aggregation at a rate which was controlled by dimer formation, but only if O2 dimers diffused more rapidly than Oi atoms and if the dimers and other small clusters dissociated easily at higher temperatures. A comparison of the deduced Oi diffusion coefficients, with those deduced from the relaxation of stress-induced dichroism, implied enhancement factors of 3 to 10 at 350C. This was attributed to the presence of grown-in H; consistent with the much greater effect of sample pre-annealing in H2 gas at 1300C. The Oi diffusivity could also be enhanced by the trapping and subsequent dissociation of rapidly diffusing dimers. It was suggested that thermal donors could be associated with O clusters that contained up to 10 Oi atoms.

R.C.Newman, M.J.Binns, C.A.Londos, S.A.McQuaid, J.H.Tucker: Solid State Phenomena, 1996, 47-48, 247-58