Investigation of the evolution of free carriers during femtosecond laser-induced ultrafast amorphization in nitrogen doped Ge₂Sb₂Te₅ films

Abstract

The femtosecond laser-driven ultrafast evolution of free carriers during the phase-change process of N-doped Ge2Sb2Te5 (N-GST) film was studied in this paper. And mechanism of initial absorption peak was calculated by two-temperature model. We found that the formation of Ge-N weaken the initial optical absorbance and decreased the concentration of free carriers, then improved the temperature of crystallization in N-GST. The doping(N) can reduce the grain size because of the easing of optical energy absorbance. At last, we inferred that, if the incident laser fluence is enough for phase transformation point, the transformation velocity of N-doped GST is faster than GST.

Pulse-to-pulse ultrafast dynamics of highly photoexcited Ge2Sb2Te5 thin films

“…In observing the relaxation dynamics of photoexcited states, we select infrared wavelengths (1000 and 1300 nm) for pump and probe pulses, which are near the band gap energy of GST and could capture plasma responses, carrier relaxation, and structural deformation. [45][46][47] The relaxation process of the excited states is important to understand the dissipation of excited energy deposited onto the sample, which will trigger the formation of LIPSS, ablation, and thermalization.…”