The annealing of the defects which were introduced by 3MeV electron irradiation of Czochralski-grown material was studied by means of positron lifetime measurements. Several annealing processes were identified by comparison with previous electron paramagnetic resonance results. The activation energies were also deduced from an analysis of isothermal annealing. It was found that di-vacancies disappeared, at about 250C, to form divacancy-O (v2O) complexes. The activation energy for the annealing of di-vacancies was estimated to be 1.30eV. The v2O complexes disappeared, at about 400C, to form trivacancy-O (v3O) and divacancy-dioxygen (v2O2) complexes. The activation energy for the annealing of v2O complexes was estimated to be 2.14eV. The v3O and v2O2 complexes disappeared, at about 440C, to form trivacancy-dioxygen (v3O2) complexes. The activation energy for the annealing of these defects was estimated to be 2.23eV. The v3O2 complexes disappeared at around 475C. The activation energy was estimated to be 2.56eV. The annealing of di-vacancies, vacancy-O and vO2 complexes was also monitored by measurements of their infra-red absorption. Temperature-dependent changes in the absorption coefficient, due to di-vacancies, were in good agreement with temperature-dependent changes in the positron trapping rate due to di-vacancies. Positron trapping at vacancy-O and vO2 complexes was not detected.

A.Kawasuso, M.Hasegawa, M.Suezawa, S.Yamaguchi, K.Sumino: Applied Surface Science, 1995, 85, 280-6