Linear and Nonlinear Optical Properties of Few-Layer Exfoliated SnSe Nanosheets

Monochalcogenides of group IV elements have been considered as phosphorene analogs due to their similar crystal and electronic structure. Here, few-layer SnSe nanosheets are synthesized by a sonication-assisted liquid phase exfoliation process and their linear and nonlinear optical properties are examined. The as-exfoliated few-layer (FL) SnSe demonstrates layer thickness from 2 to 10 nm and lateral size of 150 nm with high crystallinity. Optical measurement confirms the layer-number dependent bandgap, which is also corroborated by first-principle calculation. In addition, the FL SnSe shows a transition from saturable absorption to reverse saturable absorption with the increase of pumping power, and the nonlinear absorption is characterized by an ultrafast response time of picosecond scale. The nonlinear optical response in FL SnSe could be explained by defect-involved recombination of photogenerated carriers as well as the Auger scattering process, which is further enhanced by structural two-dimensionality.