High Anisotropic Optoelectronics in Two Dimensional Layered PbSnX2 (X = S/Se).

We systematically study the giant anisotropic optoelectronics in layered PbSnX2 (X = S/Se). The highly anisotropic optoelectronics mainly originates from the asymmetric sublattices SnX, resulting in the anisotropy of photoelectronic properties with fascinating visible light absorption range in single-layer and bilayer PbSnX2. We employ uniaxial strain in both the x and y directions and find an indirect-to-direct band gap transition, while the quasiparticle indirect band gap presents excellent linear scaling with biaxial strain in monolayer PbSnX2. We also demonstrate ultrahigh anisotropic mobilities of electrons (μy > μx) and holes (μx > μy) in both single-layer and bilayer PbSnX2 (X = S/Se), and spin-orbit coupling effects and the increase of layer number significantly reduce exciton binding energies and band gaps. Finally, the strong layer dependence of the band structure is clearly seen when the film thickness is less than 4 layers. Our results provide a fundamental understanding of highly anisotropic PbSnX2 (X = S/Se) and show two potential candidates in photoelectric applications.