POSITRON-ANNIHILATION IN ELECTRON-IRRADIATED SIXGE1-X BULK CRYSTALS

Position lifetime measurement for SixGe1-x bulk crystals has been perf ormed. The bulk lifetime of positron in the crystals varied between th ose for Ge and Si. The dependence of the lifetime on the alloy composi tion showed an abrupt change at x=0.17-0.20 which seems to be correlat ed with that of the band gap energy. After 3 MeV electron-irradiation, vacancy-type defects giving rise to the lifetimes of similar to 280 a nd similar to 330 ps were detected for 0.63 less than or equal to x le ss than or equal to 0.82 and 0.20 less than or equal to x less than or equal to 0.40, respectively, but not for x less than or equal to 0.17 . The composition-dependent vacancy production was interpreted in term s of the thermal stability of vacancies with the composition. (C) 1997 American Institute of Physics.