In this study, we applied femtosecond laser processing of Ge_1-ySn_y (y=0.08) alloys grown by MBE on Ge/Si substrates. The RSM method revealed that laser processing led to the partial compressive strain relaxation of the GeSn epilayer depending on laser radiation intensities. Our previous study related to nanosecond laser processing of Ge_1-ySn_y (y=0.04) alloys revealed the increase of Sn atomic concentration, up to 14% at the surface layer and explained by the thermogradient effect [1]. At the same time, femtosecond laser radiation almost did not change the content of Sn atoms in the GeSn layers. SEM and AFM imaging provided evident microstructure changes and formation of LIPSS [1] at higher laser intensities. The obtained reduction of the residual mechanical stress on the near-surface GeSn layers after femtosecond laser treatment can be explained by the “plasma annealing model” in the semiconductor, first proposed by J.A. Van Vechten [2]. According to this model, the reduction of the residual mechanical stress is due to the “softening” of the semiconductor lattice at the non-equilibrium charge carriers concentration comparable to the concentration of atoms in the lattice, created before reaching the melting threshold.

[1] P.Onufrijevs, et al., Opt.Laser Technol.128 (2020)106200.

[2] J.A. Van Vechten, R. TSU and FV Saris. Letters from physics. 1979, volume 74A, number 6, p. 422-426.