Detrapping of positrons and thermal stability of phosphorus-vacancy pairs in silicon

Positron-lifetime measurements have been performed on heavily P-doped (10²⁰ P/cm³) Czochralski-grown Si between room temperature and 1200?deC. Phosphorus-vacancy pairs formed in the sample show the characteristic lifetime of positrons in monovacancies, but a considerably lower binding energy (0.93±{}0.15 eV) for the positron in the trap than in free vacancies ({≥}1.6 eV). For the first time direct evidence for detrapping of positrons out of vacancy-type defects is obtained. Furthermore the phosphorus-vacancy pairs are found to be stable up to at least 1200?deC.