Direct observations of the vacancy and its annealing in germanium

Abstract

Weakly $n$-type doped germanium has been irradiated with protons up to a fluence of $3\ifmmode\times\else\texttimes\fi{}{10}^{14}$ cm${}^{\ensuremath{-}2}$ at 35 K and 100 K in a unique experimental setup. Positron annihilation measurements show a defect lifetime component of 272$\ifmmode\pm\else\textpm\fi{}$4 ps at 35 K in in situ positron lifetime measurements after irradiation at 100 K. This is identified as the positron lifetime in a germanium monovacancy. Annealing experiments in the temperature interval 35--300 K reveal two annealing stages. The first at 100 K is tentatively associated with the annealing of the Frenkel pair, the second at 200 K with the annealing of the monovacancy. Above 200 K it is observed that mobile neutral monovacancies form divacancies, with a positron lifetime of 315 ps.