Bulk solidification and recalescence phenomena in amorphous Ge films upon picosecond pulsed laser irradiation

Melting and rapid solidification are induced in amorphous Ge films upon irradiation with 10 ps laser pulses at 583 nm. The role of heat flow during the solidification process was investigated by comparing the behavior of films grown on substrates with different thermal properties. The melting and solidification kinetics are followed in real time by reflectivity measurements in the nanosecond time scale and the induced structural changes are analyzed by means of Raman spectroscopy in micro-Raman configuration. If the thermal diffusivity of the substrate is high enough, the film reamorphizes via bulk nucleation of the amorphous phase from the melt. When the thermal diffusivity of the substrate is reduced, the initial nucleation of the solid phase leads to an increase in the liquid temperature (recalescence) and in the melt duration, thus promoting the formation of the crystalline phase.