The annihilation of grown-in defects in Czochralski-type material was investigated, during O out-diffusion, by making positron measurements using a variable-energy beam. It was found that the diffusion length of the positrons became greater as the annealing time was increased, although the line-shape parameter was constant. The data on diffusion lengths, based upon the so-called semi-trapping phenomenon (and including the formation of positron Rydberg states between positrons and defects), was more sensitive to the presence of minute defects. An increase in diffusion length indicated that the grown-in defects were annihilated. The concentration of annihilated defects, related to O clusters, decreased to one tenth of that in as-grown crystals. The grown-in defects annihilated at temperatures of the order of 1150C.

T.Kitano, S.Saito, S.Tanigawa: Applied Physics Letters, 1994, 65[19], 2434-6