In situ doping effect in monolayer MoS₂ via laser irradiation

Two-dimensional (2D) semiconducting materials with a single atomic layer display exceptional structural symmetry and band structures, making them the most promising candidates for investigating the spin-valley coupling effect and fabricating novel optoelectronic devices. Their atomic thinness also makes it easy to adjust their excitonic optical response through plasma treatment or thermal annealing. In this study, we present a simple technique for modifying the optical properties of monolayer MoS2 by briefly exposing it to laser irradiation in ambient conditions. Initially, this exposure resulted in a nearly twofold increase in photoluminescence (PL) intensity, with the neutral exciton intensity increasing while the trion exciton intensity decreased. We propose that oxygen-related functional groups, such as O-2 and H2O from the surrounding air, adsorb onto MoS2 and extract extra electrons, which enhances exciton emission while reducing trion emission. In a subsequent stage, both exciton intensities decreased as all extra electrons were depleted. Additionally, any structural distortions or potential damage were found to decrease the PL intensity, and these changes were linked to alterations in the Raman spectra.