[en] MeV Ne⁺ ion bombardment has been employed to promote solid phase epitaxial growth (SPEG) of amorphous silicon layers at temperatures between 200-500 deg C. For temperatures less than 400 deg C, growth on (100) orientated substrates is observed to be linearly dependent on ion fluence and exhibits a thermal activation energy of 0.24 eV. At temperatures above 400 deg C, growth is non-linear with ion fluence, presumably due to competing thermally induced growth processes. These and other results presented in this paper, support a model for ion beam induced SPEG in which growth is nucleated by beam induced defects. This nucleation step is therefore envisaged to be athermal, with subsequent crystallization accounting for the observed activation energy of 0.24 eV. This leads to the speculation that nucleation is the limiting step for thermally induced epitaxy (2.7 eV activation energy), and implies that the activation energy for nucleation in this case is 2.4 eV