Bound vacancy interstitial pairs in irradiated silicon

Frenkel defects are produced by MeV electron irradiation of Si with an introduction rate of ∼1 cm-1 and we show that defect concentrations as high as 1019 cm-3 can be frozen in at 4 K. From X-ray diffraction we deduce that a large fraction of the defects is stabilized in the form of close Frenkel pairs and that the long range displacement fields of interstitial atoms and vacancies cancel nearly exactly. Additional larger defect agglomerates are observed at higher irradiation doses. The defect patterns observed after 4 K irradiations are compared to those of room temperature irradiations and the relative importance of ionization induced and thermally activated migration is discussed. Results for Cz-Si are compared to those obtained for FZ-Si and the thermal annealing is discussed with special emphasis to the reduction of the effective defect mobility by trapping reactions. (orig.)