Ultrafast Temporal-Spatial Dynamics of Phase Transition in N-Doped Ge₂Sb₂Te₅ Film Induced by Femtosecond Laser Pulse Irradiation

Element-doped phase change material (PCM) could improve the performances, e.g., better thermal stability, higher electrical resistance, and faster crystallization speed; thus, the influence of the doping element needs to be further investigated. In this paper, a femtosecond laser, which could realize the ultrafast phase transition rate of PCM between amorphization and crystallization, was used to explore the properties of nitrogen-doped Ge₂Sb₂Te₅ (GST), and a bond effect was proposed. The pure GST and different nitrogen contents of doped GST films were investigated by femtosecond laser pulse excitation through a pump–probe shadowgraph imaging technique. The results showed that the element-doped films could change photon absorption because of the increase in free carriers. This caused the faster rate of reflectivity to change in the irradiated area by the laser beam as the more nitrogen doped. When the nitrogen content increased, the crystallization evolution became harder because it enhanced the bond effect, which suppressed crystalline grain growth and improved the thermal stability. Based on the analysis in the paper, the desired performances of PCMs, e.g., ultrafast dynamics, crystallization evolution, and thermal stability, could be controlled according to the demands by modifying the bond effect.