Azimuthal angle dependent dielectric function of SnS by ellipsometry

Since α-SnS has optically strong anisotropic characteristics, a simple method to determine its crystal orientation is strongly needed in device engineering. In this report, by measuring dielectric function ε = ε₁ + iε₂ of α-SnS in the 1–5 eV spectral region with the full azimuthal angle range, we could find a simple relationship between measured dielectric function values and the orientation of the α-SnS crystal axis. Therefore, during the device manufacturing process, one can use spectroscopic ellipsometry to quickly measure the dielectric response of the α-SnS region of the device to correctly orient the SnS along the preferred direction for the best performance of the device. We also performed the azimuthal angle-dependent analysis of the critical points (CP) analysis, which shows that the positions of CP energies are basically invariant, while their amplitudes and lineshapes strongly depend on the azimuthal angle.