New evidence was presented for the distinct nature of A (B) and A' micro-defects in dislocation-free crystals. Dislocation-free tetra-crystals, which consisted of 4 identical grains with a [122] growth axis and second-order twin boundaries, {112}/{122}, were grown by using the Czochralski technique. These crystals were grown under growth conditions which were suitable for producing transitions between interstitial-type and vacancy-type defects. The types and distributions of grown-in and thermally-induced micro-defects were determined by means of preferential etching and X-ray topography. It was noted that the {122}/{122} twin boundary affected the distribution of grown-in micro-defects. That is, interstitial A-type and B-type defects were absent from a broad zone near to the boundary; and from the boundary itself. No depletion zone was observed in the case of A' defects, which were thought to arise from vacancy-O agglomeration. In the twin boundary, an increased density of etch pits due to A' defects was revealed. The observations were explained in terms of the selective interaction of twin boundaries with vacancies and self-interstitials during crystal growth. It was suggested that this could be used to separate vacancies from self-interstitials during crystal growth or diffusion experiments.

N.I.Puzanov, A.M.Eidenzon: Journal of Crystal Growth, 1997, 178, 459-67