Optische Datenspeicherung mit Phasenwechselmedien - Geschwindigkeitsbestimmende Prozesse der Phasenumwandlungen in Ge$_{2}$Sb$_{2}$Te$_{5}$

The amorphization and crystallization process of Ge$_{2}$Sb$_{2}$Te$_{5}$ is characterized. This alloyis used for optical data storage utilizing laser induced structural phase transitions. Thecombination of optical investigations and atomic force microscopy provides a clear pictureof the physical processes determining the write (amorphization) and erase (crystallization)velocity which defines the maximum possible data transfer rate.Amorphization is initiated as soon as a characteristic temperature is reached. Usingto element analysis of the emerging temperature profile under laser heating, this temperatureis identified as the bulk melting temperature of Ge$_{2}$Sb$_{2}$Te$_{5}$. No evidence for kineticsuperheating is found. Correspondingly, the subsequent growth of the amorphous phasetrolled by the propagation of the melting temperature isotherm. The crystallizationof as deposited amorphous Ge$_{2}$Sb$_{2}$Te$_{5}$-films requires a minimum time of (100 ± 10) ns,which is the minimum incubation time for the formation of critical nuclei. In contrastthe complete crystallization of melt-quenched amorphous bits is possible in 10 ns. This is attributed to the presence of quenched-in nuclei inside the amorphous bit