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

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.