Dielectric Function and Critical Points of SnS_0.52Se_0.48 in the Temperature Range from 27 to 350 K

We report the dielectric function ε = ε₁ + iε₂ and the critical point (CP) energies of the orthorhombic SnS_0.52Se_0.48 alloy for the zigzag (a)and thearmchair(6) directions in the spectral energy range from 0.74 to 6.42 eV and the temperature range from 27 to 350 K using spectroscopic ellipsometry. The CP energies were determined from the 2^nd derivative spectra by using the standard analytic method. We observed sharpenings and blue-shifts of the CPs with decreasing temperature. We found thirteen and twelve CPs for the a-and the b-directions, respectively, at the lowest temperature while only eight and nine CPs were detected at room temperature. Also, an exciton effect was observed only in the armchair direction at low temperatures. The temperature dependences of the CP energies were determined by fitting the data to a phenomenological expression that contain the Bose-Einstein statistical factor and the temperature coefficient to describe the electron-phonon interaction.