Minimum time for laser induced amorphization of $Ge2Sb2Te5$ films

The minimum time t required to form an amorphous spot in a crystalline film of $Ge2Sb2Te5$ with NaCl structure was investigated for various applied laser powers P. An elementary power law of the form $P∝t−0.5$ is observed for pulse lengths larger than 10 ns which shows that amorphization occurs as soon as the melting temperature is reached. This implies that kinetic superheating does not occur on this time scale. The growth velocity of amorphous marks was inferred from atomic force microscopy (AFM) both parallel and perpendicular to the film plane. The growth in the vertical direction is shown to dominate the change in reflectivity and thus the size of the readout signal of data storage devices. The experimental data are compared with numerical calculation of the temperature field using finite element analysis. These calculations determine the position of the melt temperature isotherm and reproduce the depth and the area of the amorphous regions as inferred from AFM data.