Production of Divacancies and Vacancies by Electron Irradiation of Silicon

A study is described of the dependence of the room-temperature production of divacancies and vacancies in silicon upon the energy of the bombarding electrons over the range 0.7-56 MeV. For the divacancy, the Si-G6 electron-paramagnetic-resonance spectrum associated with the singly positively charged state of the defect was monitored. As a monitor for single-vacancy production, the Si-B1 center due to the oxygen-vacancy pair was used. Over the energy range 0.7-1.5 MeV, the divacancy production rate rises a factor of 7 while the single-vacancy rate rises only a factor of 1.5, reflecting a higher threshold for divacancy production, as expected. Also presented are data on the dependence of the divacancy production rate on the orientation of the crystal axes with respect to the incident beam and on the resulting anisotropy of the divacancy orientation in the lattice. The results of the anisotropy studies are shown to be consistent with a simple microscopic model of the damage event.