Diffuse X-ray scattering from Czochralski-grown crystals was investigated after annealing (450C, 24h). The X-ray measurements were made, near to the (400) and (3¯11) Bragg reflections, in directions that were parallel and perpendicular to the scattering vector. All of the characteristic features were predicted by the theory of scattering from defect clusters with weak displacement fields (Huang scattering). It was shown that the long-range part of the displacement fields had orthorhombic symmetry, and that the defects were of interstitial type. By comparing the symmetry of diffuse scattering intensities with those of displacement fields around thermal donor models for Czochralski-grown Si, it was shown that an NL8 or IO2 (self-interstitial plus two O atoms) model would be a reasonable core structure for the thermal donors.

T.Yamazaki, I.Hashimoto: Physical Review B, 1997, 56[9], 5228-34