Selective interaction of twin boundaries with vacancies and self-interstitials in dislocation-free Si tetracrystals

We report a new evidence for distinct nature of A (B) and A' microdefects present in dislocation-free Si crystals. Dislocation-free Si tetracrystals, which consist of four identical grains with the [1 2 2] growth axis and with the second-order twin boundaries {1 2 2}/{1 2 2}, are grown by the Czochralski (CZ) technique. The tetracrystals are grown under appropriate growth conditions to attain the transition between the interstitial- and vacancy-type defects. The type and distribution of grown-in and thermally-induced microdefects are examined by preferential etching and X-ray topography. The {1 2 2}/{1 2 2} twin boundary influences the distribution of grown-in microdefects: the interstitial A- and B-type defects are absent in a broad zone near the boundary and in the boundary itself. No depletion zone is observed for A' defects, which are thought to arise from the vacancy-oxygen agglomeration. In the twin boundary, an increased density of etch pits due to A' defects is revealed. We interpret these observations in terms of the selective interaction of the twin boundary with vacancies and self-interstitials during crystal growth. This phenomenon can be used to separate vacancies from self-interstitials during crystal growth or diffusion experiments.