INTRINSIC-DEFECT AND EXTRINSIC-DEFECT FORMATION IN SILICA GLASSES BY RADIATION

The dose dependence of the defect concentration produced by radiation was studied for many types of silica glass in order to discuss the con tribution of 'extrinsic' and 'intrinsic' processes to the paramagnetic defect formation. A linearly increasing concentration of paramagnetic defects with dose accompanied by a saturating tendency is observed fo r the 'extrinsic' defect formation due to transformation of pre-existi ng precursors. The concentration of E' centers substantially equals th at of non-bridging oxygen hole centers, and both are approximately pro portional to the square-root of the accumulated dose for the 'intrinsi c' defect formation involving cleavage of the Si-O network. Since the dose dependence of the defects is independent of the incident photon e nergy, electron-hole pairs having the band gap energy of silica are im plied to have an essential role for either 'extrinsic' or 'intrinsic' defect formation.