The ultrahigh doping levels of Si needed in ultradownscaled electronic devices can be achieved forming supersaturated solid solutions by solid-phase epitaxy. These solutions are, however, unstable upon high-temperature annealing, and electrical deactivation of the impurities exceeding the solid solubility limit occurs. There are indications that deactivation is driven by the interaction of impurities with native (ie, intrinsic) defects, but the relevant process has not been studied in detail thus far, nor have the defect complexes presumably causing the deactivation been identified. Here we use light-ion beam treatments and Rutherford backscattering analysis combined with first-principles density-functional calculations to investigate the interaction of a specific Group-III acceptor, Ga, with native defects—mostly self-interstitials—generated by irradiation at room temperature, or upon thermal annealing. Monitoring the off …