Femtosecond laser-induced ultrafast transient snapshots and crystallization dynamics in phase change material

Abstract

We report here femtosecond laser-driven transient snapshots of ultrafast crystallization of Ge2Sb2Te5 films from its as-deposited amorphous phase, and the local structural change is validated by micro-Raman spectroscopy and x-ray diffraction. The decay time constant of ∼5 ps in transient spectra with a precise temporal resolution using 400 nm (pump) reveals about 68 volumetric percentage crystallization at a remarkably low fluence of 4.78 mJ · cm−2. This is attributed to reiterated excitation after a complete carrier relaxation and formation of a long-lasting transient phase at sub-threshold fluences. Furthermore, Raman spectra of irradiated spots confirm defective-octahedral modes at 110 and 160 cm−1 validating crystallization. © 2017 Optical Society of America.