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 lase r powers P. An elementary power law of the form P proportional to t(-0.5) i s observed for pulse lengths larger than 10 ns which shows that amorphizati on 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 pa rallel and perpendicular to the film plane. The growth in the vertical dire ction is shown to dominate the change in reflectivity and thus the size of the readout signal of data storage devices. The experimental data are compa red with numerical calculation of the temperature field using finite elemen t analysis. These calculations determine the position of the melt temperatu re isotherm and reproduce the depth and the area of the amorphous regions a s inferred from AFM data. (C) 2000 American Institute of Physics. [S0021-89 79(00)06814-6].