Metal Contact Engineering for Nonlinear Optics and Carrier Dynamics in Monolayer MoS 2

ABSTRACT Two‐dimensional transition metal dichalcogenides (TMDCs) are promising optoelectronic materials, yet their charge transport is highly sensitive to metal‐semiconductor contacts. Here, we demonstrate that the number of contact edges in metal/MoS 2 junctions serves as an effective tuning parameter for carrier injection, exciton dynamics, and nonlinear optical responses. Using Mo and Cr contacts with single‐, double‐, and triple‐side configurations, we show that Mo contacts provide more efficient electron injection due to a lower effective Schottky barrier, converting neutral excitons into negative trions and suppressing photoluminescence. Second‐harmonic generation reveals a sixfold enhancement of χ ( 2 ) for triple‐side Mo contacts, while I‐scan measurements confirm effective modulation of third‐order nonlinearity. Transient absorption spectroscopy and fluorescence lifetime imaging reveal a synergistic mechanism in which injected carriers simultaneously promote trion formation and saturate defect states, extending carrier lifetimes from ∼19 to 37 ps. First‐principles calculations and temperature‐dependent device simulations further validate the atomistic origin of the enhanced charge transfer and the presence of thermally activated interface trap states. Furthermore, this study elucidates the modulation mechanism of metal contacts through band alignment, interfacial coupling, and carrier transport, providing a foundation for interface engineering of 2D material‐based optoelectronic devices.