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

Abstract

Experimental results on positron trapping at vacancies in electron-irradiated silicon are presented. The positron lifetimes 273\ifmmode\pm\else\textpm\fi{}3 and 248\ifmmode\pm\else\textpm\fi{}2 ps in pure Si and heavily-phosphorus-doped Si ([P]=${10}^{20}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$) are assigned to a negative monovacancy ${V}^{\mathrm{\ensuremath{-}}}$ and a negative vacancy-phosphorus pair (V-P${)}^{\mathrm{\ensuremath{-}}}$, respectively. In pure Si, positron trapping displays a strong negative temperature dependence, and the specific trapping rate reaches very large values ${(10}^{17--}$${10}^{18}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$) 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.