Continuous downscaling of complementary metal-oxide semiconductor devices requires the manufacture of highly doped ultrashallow junctions. A preamorphizing implant (PAI) is commonly used in industrial processing in order to avoid unfavorable profile broadening and channeling tails during dopant atom implant in the ultralow energy regime (<5 keV). In this work, we report about a detailed characterization of the structural changes induced by xenon PAI treatment on ultralow energy arsenic-implanted (001) silicon. Combined x-ray scattering methods, medium energy ion scattering, and transmission electron microscopy are applied to obtain as comprehensive picture as possible of the reordering processes occurring during the postimplantation annealing treatment. Evidence is found that end-of-range defects, present after implant below the amorphous-to-crystalline interface, transform from small Si interstitial clusters to dislocation loops during annealing depending on the implant conditions. Simultaneously, As atoms redistribute by moving to the substitutional sites of the freshly regrown Si lattice without inducing a local residual strain field. The remaining fraction of electrically inactive dopants cumulates in a subnanometer-thick layer beneath the surface oxide.