The behavior of vacancy clusters in neutron transmutation-doped samples was investigated by means of Fourier transform infra-red spectroscopy and photo-induced transient spectroscopy. The Fourier transform infra-red spectroscopic results showed that infra-red absorption peaks, at 707, 742 and 776/cm, appeared during the annealing of these samples at temperatures ranging from 350 to 600C. By comparing the present results with previous data, the defect center (termed the P0 center) which gave rise to these infra-red absorption bands, was assumed to be a multi-vacancy cluster that consisted of at least 6 vacancies. The use of photo-induced transient spectroscopy showed that the P0 center introduced acceptor levels at Ec - 0.427eV and Ec - 0.524eV within the energy gap.

Y.Xu, C.Liu, Y.Li, H.Wang: Journal of Applied Physics, 1995, 78[11], 6458-60