Defect Clusters in Electron-Irradiated Silicon

Calculations of the formation of disordered regions in silicon due to irradiation by high energy (15-45 MeV) electrons indicate that a sufficient concentration of defect clusters is produced to affect the electrical properties of the material. Isochronal annealing of room temperature radiation-induced degradation in the short-circuit current of silicon solar cells and in the minority carrier lifetime of the p-type base region is studied up to 500°C. The existence of a low temperature (50-200°C) annealing stage is shown to be independent of dopant and oxygen impurity concentration. It is inferred that this stage, which is similar to those observed in fast neutron- and in proton-irradiated silicon, is characteristic of cluster formation.