Interface Engineering via Carrier Injection: Regulating Nonlinear Optical and Carrier Dynamics in Monolayer MoS₂ through Metal Contacts

Two-dimensional transition metal dichalcogenides (TMDCs) are highly promising optoelectronic materials. However, their dangling-bond-free surfaces result in charge transport that strongly depends on metal-semiconductor contact characteristics. This work systematically investigates the modulation of carrier injection, recombination dynamics, and nonlinear optical properties in monolayer MoS₂ by metals with different work functions (Cr and Mo) and various contact configurations (single-, double-, and triple-edge). Through multiple characterization techniques including photoluminescence, second-harmonic generation, transient absorption spectroscopy, I-scan, and fluorescence lifetime imaging, we find that Mo contacts enable efficient electron injection due to their lower Schottky barrier and covalent interface. This promotes the conversion of neutral excitons into negative trions, thereby significantly modulating the luminescence behavior. SHG measurements show that Mo contacts enhance the second-order nonlinear susceptibility χ⁽²⁾, while I-scan results indicate that their third-order nonlinearity and saturable absorption properties can also be effectively modulated. Combined time-resolved and near-field imaging further reveal the spatiotemporal dynamics of carriers at the interface. This study elucidates the modulation mechanism of metal contacts from the perspectives of band alignment, interfacial coupling, and carrier transport, providing theoretical and experimental foundations for the interface engineering of two-dimensional material-based optoelectronic devices.