Electronic, optical and lattice dynamics properties of layered GaSe_1-xS_x

The electronic, optical and lattice dynamics properties of GaSe_1-xS_x are investigated in detail using Density Functional Theory (DFT). The results indicate that the calculated dielectric and Raman spectra are in agreement with the experimental data. As the proportion of S-atoms increases, there is an increase in the band gaps and a decrease in the lattice parameters. Further, there are reductions in both the static electronic dielectric ε₁(0) and refractive index n(0), with the lattice vibrations of Ga-X (X = Se or S) bonds gradually strengthening and shifting towards the high-frequency region. These variation tendencies indicate a gradual increase in the interaction of Ga-X bonds with the increasing ratio of S-atoms. From the differential charge densities, the inter-layer and intra-layer interactions of GaSe_0.75S_0.25 are the weakest, with those of GaS being the strongest. Due to the highly anisotropic bonding forces, optical spectra of GaSe_1-xS_x present clear polarization anisotropy in the direction of vector E. The absorption and reflectivity spectra show that GaSe_1-xS_x are transmitted when frequencies are lower than 2.36 eV(525 nm).