Ion implantation of P into (111) Si has been investigated by cross‐sectional transmission electron microscopy and secondary ion mass spectrometry. In the dose range 1×1015–2×1016cm−2at 120 keV the formation and width of the amorphous (a) layers were sensitively dependent on wafer temperature. The effect of dynamic annealing on the crystalline (c) to amorphous transformation, and the effect of amorphicity and roughness of thea/cinterface on the formation of microtwins have been studied. It has been observed that the P atoms in the amorphous (a) region do not redistribute on subsequent annealing while the P atoms below thea/crystalline (c) interface diffuse rapidly into the Si substrate. The carrier concentration profiles from the annealed samples were found to follow the atomic profiles almost exactly over the depth range extending from the surface to where the originala/cinterface existed. However, in the deeper regions, the electrical activity was found to be dependent on the annealing temperature used. The different behavior of atomic and carrier concentration redistributions in the amorphous and crystalline regions has been explained by a model that assumes incorporation of impurity atoms on substitutional sites by the movinga/cinterface on recrystallization. The P atoms in the deeper regions are believed to redistribute via an interstitial diffusion mechanism at low temperatures (≤750 °C) and eventually occupy substitutional sites at higher temperatures (>800 °C).