Evolution of quasiperiodic microstructure of Ge-Sb-Te-based films irradiated by multi-pulsed picosecond laser

In this paper, the crystal morphology and grain size evolution of Ge-Sb-Te (GST) irradiated by multi-pulsed picosecond (ps) laser were characterized by transmission electron microscopy and selected area electron diffraction. Morphologies induced by multi-pulsed laser were radially quasiperiodic structures, and the crystallization area induced by the first laser pulse acted as the periodic repeated unit. Single laser pulse irradiation produced three different conterminal annular crystallization zones, and their formation mechanisms were discussed. GST films accumulated thermal and structural change induced by per laser pulse, reducing crystallization threshold and extending crystallization fluence range. Sequentially, every subsequent laser pulse created a new crystallization area, and then accumulated to be a pulse number dependence radially quasiperiodic structure. Meanwhile, the laser pulse train dramatically refined grains. The grain boundaries are presented as an alternating-layered structure or atomic ordering domain. The present study revealed microstructure evolution of intermediate states for multi-level storage and realized multi-phase changes and is critical to enhance storage density.