Structural properties and vibrational modes of different polytypes of gallium selenide crystals (ε, β, γ, δ): insights from a DFT study

In this paper, XRD patterns and Raman spectra were determined, using the Density Function Theory, to study the structural properties and vibrational modes of the polytype of GaSe materials, ε-GaSe, β-GaSe, γ-GaSe, and δ-GaSe, in different temperatures. Room temperature X-ray diffraction (XRD) analysis revealed crystal phases consistent with those expected, and calculated unit cell parameters matched reference values. Furthermore, Raman spectroscopy for all samples yielded vibrational modes in excellent agreement with experimental data, corroborating the XRD findings. In the temperature range from 5 to 400K, the shifts of the vibrational modes were calculated for all polytypes. The thermal behavior of these shifts shows that the structures of the polytypes can undergo distortions with increasing temperature. These results suggest a first contribution to understanding the effect of temperature on the vibrational modes of the polytype of GaSe and consequently on their structures.