Abstract
Positron annihilation was used to characterize vacancy-type defects in two types of polycrystalline Si grown at temperatures above ~800 °C by chemical vapour deposition. The majority of vacancies (80%) consisted of monovacancies, and their thermal stability indicated them to be trapped at grain boundaries or at dislocations. Annealing above 500 °C caused a significant reduction in the monovacancy concentration, and an increase in divacancy concentration. Divacancies started to anneal above 1200 °C. Measurements between 8 and 293 K indicated that vacancies were neutral before as well as after annealing at 1380 °C. Fz-grown Si from one of these materials contained vacancy clusters with an average size of six to ten vacancies which persisted to 1380 °C. The cluster concentration corresponded to a monovacancy concentration of 10 15 to 10 16 cm −3 , which is at least one order of magnitude larger than estimates based on voids [R. Falster, V.V. Voronko, F. Quast, Phys. Status Solidi B 222, 219 (2000)].
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