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 (V_S, V_S2, Mo_S, V2_S2, V_Mo) 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.