Structural defects dependence of the second-harmonic generation in monolayer MoS2.

Second-harmonic generation (SHG) is emerging as a powerful tool for non-destructive material characterization. Simultaneously, it serves as a fundamental mechanism for expanding the wavelength range of laser sources. Although defects are inherently unavoidable in the synthesis of transition metal dichalcogenides like MoS2, recent studies have demonstrated that these defects can be precisely engineered. Therefore, a systematic understanding of how the type and concentration of defects influence the SHG properties of MoS2 is crucial. This study demonstrates that by selectively introducing specific point defects (VS, VS2, MoS, V2S2, VMo) and accurately controlling their density, the SHG of monolayer MoS2 can be directionally tuned across the visible to near-infrared range and even the communication bands. These findings provide a theoretical foundation for designing broadband frequency converters and communication-band SHG devices via defect engineering.