Study on the crystallization mechanism of amorphous Ge2Sb2Te5 thin films induced by a short single pulsed laser

Abstract

The crystallization mechanism in an amorphous Ge2Sb2Te5 (a-GST) thin film induced by a single pulsed laser was investigated in this paper. The finite element simulation and x-ray diffraction analysis showed that two kinds of crystallization mechanisms performed for the laser-induced phase transition of a-GST, that is, the solid-state phase transition took place at a lower laser fluence while the liquid–solid phase transition occurred at a relatively high laser fluence. Transmission electron microscopy observations showed that the microstructure in the liquid–solid phase transition was more uniform as compared to that in the solid-state phase transition because of poor atom diffusion. Crystallization characteristics at different laser fluences and film thickness were elucidated. It was found that at a lower laser fluence a thinner film had the better crystallinity owing to thermal convection, while at a higher laser fluence a thicker film showed the better crystallinity due to the release of latent heat in the liquid–solid phase transition. These findings enable a deep understanding of ultra-fast phase transition induced by laser irradiation.