Extended anisotropic phonon dispersion and optical properties of two-dimensional ternary SnSSe

Abstract

The phonon dispersion and optical properties of mechanically exfoliated SnSSe were investigated with the aid of high-resolution Raman scattering and photoluminescence (PL) spectroscopies along with first-principles calculations. The Raman modes indicate two-fold symmetry for in-plane vibrations and four-fold symmetry for out-of-plane vibrations. Consequently, the different polarization properties of the phonon modes demonstrate the anisotropic nature of SnSSe. The softening of Raman modes with the increase in temperature is described in terms of thermal expansion and anharmonic scattering, which contributes to phonon vibration, whereas a weak interlayer interaction in the SnSSe layers is observed. The significant suppression of PL signals at a higher temperature is related to the increase in the non-radiative recombination of electron–hole pairs as a result of the increment in the number of phonons and in the thermal excitation of carriers. In addition, the fabricated electrical device on few-layer SnSSe shows a significant I_ON/I_OFF ratio and good electron mobility for optoelectronic applications. These results further improve the understanding of the microscopic details of SnSSe as an important material, providing better insights to control phonon propagation in thermoelectric, photovoltaic, and other materials to induce thermal management.