The selective trapping of self-interstitials by interstitial carbon impurities in electron irradiated silicon

Float-zone silicon doped with carbon (1.6*10 17 Cm -3 ) has been irradiated with 2 MeV electrons below 220 K up to a dose of 1.9*10 18 electrons cm -2 leading to a monotonic decrease in the concentration of the substitutional impurity. Interstitial carbon is produced but its concentration saturates and then falls because the defects trap mobile self interstitials. New infrared absorption lines at 966 and 959 cm -1 (77 K) are ascribed to a C 1 -Si i pair defect which also acts as a nucleation site for agglomeration of Si 1 atoms. The latter reactions appear to occur during irradiations at 300 K.