Mass effects on regrowth rates and activation energies of solid-phase epitaxy induced by ion beams in silicon

The effect of ion mass on ion-beam-induced epitaxial crystallization of silicon has been examined for five types of ion (C, Si, Ge, Ag, Au) at energies of 1.5, 3.0, and 5.6 MeV. Regrowth rates have been normalized to the number of displacements or nuclear energy deposition at the interface to evaluate the contribution of defect generation to crystal growth. The normalized regrowth rate increased by a factor of 4 with decreasing ion mass from Au to C, showing a similar behavior to dose rate dependences previously reported at lower ion energies. However, the dose rate dependence for 3.0 MeV Au and Ag deviated from this mass dependence curve at low dose rates, indicating that significant cascade density effects (instantaneous dose rate effects) coexist with average dose rate effects. This implies that the crystal growth rate is affected by defect interactions within individual cascades as well as by defect interactions between different cascades. Activation energies measured for four types of ion at 3.0 MeV are also mass dependent and varied from 0.18 to 0.40 eV. These results indicate that ion-beam-induced epitaxial crystallization cannot be characterized by a single activation energy. Our data have been compared with a number of models for ion-beam-induced crystallization and found to be inconsistent with a process controlled by a single defect type. We suggest that several rate-limiting defect processes may be involved and the dominance of a single defect depends on the ion mass (cascade density), average dose rate, and temperature regime.