High-Resolution Microlens-Assisted Tunable n-Type Optical Doping in Monolayer MoS₂

Atomically thin two-dimensional transition metal dichalcogenides (2D TMDCs), especially monolayer MoS₂, have garnered considerable attention as promising materials for next-generation transistors. However, their large surface-to-volume ratio renders them highly sensitive to defects, underscoring the need for selective, localized, and precise control of their defect profiles. Here, we introduce a laser-assisted microlens array processing (LAMP) technique that enables highly localized n-type optical doping of monolayer MoS₂ by utilizing self-assembled polystyrene microspheres as microlenses to focus a 532 nm continuous-wave laser below the diffraction limit. Under low laser powers (40-60 mW), sulfur vacancies are selectively generated without inducing global thermal damage, allowing systematic control of the vacancy concentration. Spectroscopic analyses reveal electron-donor-like defects and tunable vacancy density. MoS₂ transistors treated by LAMP exhibit finely tunable doping, yielding up to a 51-fold increase in field-effect mobility and a 37-fold increase in carrier density, with the enhanced n-type characteristics remaining stable for several weeks. Unlike direct laser irradiation, LAMP offers high spatial resolution, low energy consumption, and reproducible vacancy engineering while minimizing thermal damage. This complementary metal-oxide-semiconductor-compatible strategy provides a robust post-fabrication approach for precise electronic property tuning in two-dimensional transition metal dichalcogenide devices.