Phonon shifts which were related to the defect structure of neutron transmutation-doped semi-insulating material were studied by using Raman scattering and X-ray diffraction methods. The defect structure was considered for 2 cases of vacancy interstitials and antisites by using a simple model for LO-TO phonon frequency splitting. It was suggested that a slight reduction in the latter arose from vacancy-interstitial clusters rather than from antisite defects when account was taken of the volume expansion, antisite defect concentrations, and displaced atoms in neutron-irradiated samples. The clusters were associated with a volume expansion of about 0.4% in neutron-irradiated samples.

K.Kuriyama, S.Satoh, M.Okada: Physical Review B, 1996, 54[19], 13413-5