Solidification phenomena in Ge films upon nano- and pico-second laser pulse melting

Abstract

Melting has been induced in amorphous Ge films upon irradiation with both nano- and pico-second laser pulses. The role of undercooling and heat flow in the subsequent rapid solidification process has been investigated by analyzing the behavior of films with different thicknesses (30-180 nm) grown on Si(100) substrates by means of real time reflectivity measurements in the ns timescale. Recalescence is observed in films with a thickness above a threshold value which depends on the pulse duration. An additional solidification scenario, i.e. surface initiated solidification, is observed upon ps pulse irradiation in films with intermediate thicknesses.