| Summary: | Molybdenum disulfide (MoS<sub>2</sub>) has been actively explored as a direct bandgap semiconductor in the monolayer (ML) limit for various applications due to its prominent physical properties and stability. In order to broaden its application range further, diverse treatments have been developed to modulate the properties of ML-MoS<sub>2</sub>. The native point defects, such as S vacancies, are known to activate surface charge transfer doping in ML-MoS<sub>2</sub>. Unlike conventional semiconductors, ML-MoS<sub>2</sub> shows distinct excitonic transitions that can be exploited for controlling its optical, optoelectronic, and electric characteristics via coupling with defect-driven doping. Here, the ambient photoluminescence (PL) of ML-MoS<sub>2</sub> could be increased by ~1500% at the center of focused-laser irradiation (FLI). Expectedly, the PL intensity varied spatially along with exciton–trion transitions across the irradiation spot due to the Gaussian profile of laser intensity. Then, nano-Auger electron spectroscopy (n-AES) revealed that the spectral fraction of exciton PL increased by ~69.2% while that of trion PL decreased by ~49.9% with increasing S deficiency up to ~13.4 ± 3.5%. Cryogenic PL and field-effect transistor experiments were also performed to understand the defect-related phenomena comprehensively. This novel experimental combination of FLI with an n-AES probe provides a facile, effective, and cost-efficient approach for exploring defect effects in two-dimensional structures.
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