Dynamics of laser induced phase transformations in amorphous silicon

The kinetics of the crystallization process in amorphous hydrogenated Si (a-Si:H) thin films induced by XeCl and ArF excimer laser pulses has been studied both experimentally and theoretically. Time-resolved reflectivity spectroscopy (TRR) has been used to monitor phase changes as a function of pulse energy density. The time of the recrystallization process, tr, has been determined experimentally. Independently of the wavelength of applied laser radiation, a strong minimum has been found in the tr versus energy density (E) curves. The theoretical simulations have been done with the non-equilibrium thermal model which includes a nucleation process. The results clearly demonstrate that the crystallization from the phase interface dominates for energy densities close to the melting threshold in contrast to the high energy density region where the nucleation and solidification in the subsurface region prevails.