Annealing processes of vacancies in silicon induced by electron irradiation: analysis using positron lifetime measurement

Annealing processes of vacancies in posphorus doped FZ-Si induced by 15MeV electron irradiation were studied with positron lifetime measurements. It was found that as-irradiated Si contained mainly vacancy-phosphorus pairs (VP) and divacancies (V2) which gave rise to the positron lifetimes 248ps and 320ps, respectively. Several annealing processes were identified: VP pairs disappeared around 150 C. The mobile vacancies released from VP formed V3 and V2 . V3 decomposed into V and V2 below 200 C. The mobile V2 disappeared around 300 C to form V4 (350ps). V4 dissociated around 350 C to form V6 (400ps). V6 dissociated around 400 C to form larger vacancy clusters (500ps). Thus, it was concluded that vacancy clusters consisting of even number of vacancies were formed after annealing out of V2. The positron lifetimes 248(VP), 320(V2), 350(V4), and 400(V6) ps identified at present work were in good agreement with the theoretical dependence of lifetimes on the cluster size. (orig.)