We compare the defect complexes generated in crystalline Si by electron irradiation and ion implantation, using irradiation fluences which deposit the same total energy in nuclear collisions. Deep level transient spectroscopy was used to monitor both vacancy-type (e.g., divacancies) and interstitial-type (e.g., carbon–oxygen complexes) defects produced on p-type Si samples. We show that identical defect structures and annealing behavior, T ⩽ 300 °C, are produced by both Si implantation and electron irradiation. After annealing at higher temperatures, we observe a higher residual damage in ion implanted samples, which is a direct consequence of the extra incorporated ions. We demonstrate that the substrate impurity content rather than the ion cascade dominates defect formation and evolution. In high purity Si, B-related instead of C-related (e.g., the carbon–oxygen complex) defects preferentially store the interstitials which escape direct recombination with vacancies, and the thermal stability of the CiOi complexes is decreased in Si containing low concentration of impurities. © 1997 American Institute of Physics.