It was noted that current understanding of the vacancy-O pair (A center) was quite satisfactory, but that its annealing behaviour exhibited some features which required a better explanation. An investigation was therefore made of the evolution of the infra-red signal of the center (828/cm) which was created in Czochralski-type samples by neutron irradiation. The amplitude of the band appeared to be stable at up to 200C, where it began to increase and reached a maximum value at about 280C, and then began to decrease rapidly up to about 400C; although a trace of it lingered in the spectra at up to 550C. The inverse annealing stage (200-280C), the kinetics of the annealing out (300-400C) and the stabilization of the defect signal (400-500C) were of particular interest. It was found that, after completing the annealing sequence, and re-irradiating the material, the inverse annealing stage was absent. This led to the suggestion of an unknown defect which competed with Oi in capturing vacancies. The stabilization of the 828/cm band amplitude above 400C was tentatively attributed to the trapping of a number of A-centers near to disordered regions or large defects. This resulted in a larger binding energy of the corresponding defects.

C.A.Londos, N.V.Sarlis, L.G.Fytros: Solid State Phenomena, 1997, 57-58, 245-50