Photoluminescence enhancement in two-dimensional semiconductors via spacer-free metallic screening

Abstract

Excitons in monolayer transition metal dichalcogenides (TMDCs) are highly sensitive to their environment, allowing for screening to modulate exciton radiative recombination and photoluminescence (PL) intensity. While previous studies have explored modifying the dielectric environment and introducing metals separated from TMDCs by a dielectric spacer to influence screening effects and PL, the case where a metal is in contact with the TMDC monolayer by a van der Waals gap—has not been demonstrated. Here, we demonstrate that a metal layer in contact with the TMDC monolayer through a van der Waals gap achieves significant PL enhancement. By stacking metals with appropriate workfunctions above or below a TMDC monolayer, we achieved up to two-orders-of-magnitude increase in PL intensity. This enhancement is due to reduced exciton-exciton interactions from strong screening by the metal layer. Our measurements show reduced exciton-exciton annihilation, even at high generation rates, facilitated by the metal’s strong screening effect.