The thermal transmission process induced by single-shot femtosecond laser pulses in Sb<sub>70</sub>Te<sub>30</sub> phase change thin films with or without a Ag thermal-conductive layer was studied numerically with a two-temperature model. The distribution of electron and lattice temperatures was calculated by a one-dimensional finite difference method. The different temperature evolution characteristics on different time scales (from several picoseconds, to tens of picoseconds and to several nanoseconds) are discussed based on the electron-phonon coupling theory. The influence of a special point in the lattice temperature evolution curves on the crystallization time of phase change thin films is analyzed. The results will be helpful to the deeper understanding of the ultrafast phase transition mechanism of phase change memory materials.
The Femtosecond laser pulse induced phase transition dynamics of Cr-doped Sb<sub>2</sub>Te<sub>1</sub> films was studied by real-time reflectivity measurements with a pump-probe system. It was found that crystallization of the as-deposited Cr<sub>x</sub>Sb<sub>2</sub>Te<sub>1</sub> phase-change thin films exhibits a multi-stage process lasting for about 40ns.The time required for the multi-stage process seems to be not related to the contents of Cr element. The durations of the crystallization and amorphization processes are approximately the same. Doping Cr into Sb<sub>2</sub>Te<sub>1</sub> thin film can improve its photo-thermal stability without obvious change in the crystallization rate. Optical images and image intensity cross sections are used to visualize the transformed regions. This work may provide further insight into the phase-change mechanism of Cr<sub>x</sub>Sb<sub>2</sub>Te<sub>1</sub> under extra-non-equilibrium conditions and aid to develop new ultrafast phase-change memory materials.