Positron trapping at vacancies in electron-irradiated Si at low temperatures

Experimental results on positron trapping at vacancies in electron-irradiated silicon are presented. The positron lifetimes 273 3 and 248 2 ps in pure Si and heavily-phosphorus-doped Si ([P]=1020 cm-3) are assigned to a negative monovacancy V- and a negative vacancy-phosphorus pair (V-P)-, respectively. In pure Si, positron trapping displays a strong negative temperature dependence, and the specific trapping rate reaches very large values (1017 1018 s-1) at low temperatures. In Si:P the trapping rate is independent of temperature. These different temperature behaviors are attributed to different positron-trapping mechanisms, a cascade of one-phonon transitions in pure Si, and an Auger process in Si:P.