The interplay between neutral and charged excitons driven by electron irradiation in monolayer WSe2

Abstract

Thanks to their strong excitonic effects and tunable bandgap, two-dimensional transition metal dichalcogenides (TMDs) are the key elements of many micro-optoelectronic, photonic, and next-generation logic devices. The performance optimization of current devices and the development of novel systems have recently boosted the engineering of the optical and electronic properties of the TMDs to externally control the dynamics of their excitons, including exciton formation, interaction, and relaxation. Among the various regulation strategies, electron-irradiation is a facile and deterministic process. Here, we employ this method to regulate the interplay among neutral and charged excitons in monolayer WSe${}_2$ by varying the electron dose. Specifically, we demonstrate that the interaction of 20 keV electrons with the lattice of WSe${}_2$ crystals and the subsequent exposure to ambient air causes the tuning of the charge doping and the formation of a compressive strain field. Their simultaneous actions result in a conversion of neutral excitons into charged ones, while their single contribution is qualitatively disentangled by correlating the binding energy with the excitons intensities. These findings significantly advance our understanding of the WSe${}_2$ optical emission properties engineered by electron-irradiation, shedding light on the intricate interplay between the excitons.