The structure of silicon layers implanted with high current As’ beams at different power densities under self-annealing conditions (i.e. with simultaneous damage recovery activated by beam heating) has been investigated with Rutherford Backscattering and Transmission Electron Microscopy techniques. The results have been compared with previous ones obtained with P÷ implantation. They show that, in both cases, an ion-induced mechanism of recrystallization, characterized by an activation energy of the order of 0.3 eV, is operative at temperatures below the values necessary to activate thermal epitaxy. Chemical impurity profiles in samples self-annealed with As+ ions at high beam power density, show the occurrence of two relevant radiation-induced effects: i) diffusion enhancement in the tail region; ii) formation of two impurity peaks, separated by a depletion region centred at the ion projected range. While the deeper peak disappears with increasing irradiation time, the one located at the maximum of nuclear energy loss grows, apparently as a consequence of segregation of As atoms at large clusters of vacancy-type defects.