Atomic Substitution Induces Se@S Antisite Defects in SnSSe Alloy for Carrier Dynamics Reversal and Nonlinear Optical Properties Modulation

ABSTRACT This study focuses on constructing the alloyed transition metal dichalcogenide (ATMD) SnSSe from SnS 2 via atomic substitution, thereby effectively regulating its nonlinear optical (NLO) and ultrafast photonic properties. The results show that Se atoms replace some S atoms in the SnS 2 lattice, inducing lattice distortion that alters the intrinsic electronic structure of SnS 2 . Introducing Se significantly enhances orbital hybridization, narrowing the bandgap and increasing the density of states at the band edges of SnSSe. Benefiting from the unique Se@S antisite defects, the carrier dynamics of SnSSe undergo a significant reversal compared to those of SnS 2 . Meanwhile, under the synergistic effect of Se vacancies and Se@S antisite defects, SnSSe enables ultrafast trapping and rapid recombination of photogenerated carriers, thereby significantly shortening the carrier lifetime. This atomic‐substitution‐induced property reconstruction endows SnSSe with superior infrared nonlinear absorption performance relative to SnS 2 , thereby enhancing broadband laser pulse modulation. This study confirms that SnSSe is an ideal candidate for high‐performance, ultrafast photonic devices and that alloying via atomic substitution is an effective strategy for regulating the NLO and laser modulation properties of conventional TMDs.