2017，Alloying effect on bright–dark exciton states in ternary monolayer MoxW1–xSe2

Alloying effect on bright–dark exciton states in ternary monolayer MoxW1–xSe2.pdf

Abstract

Binary transition metal dichalcogenides (TMDCs) in the class MX₂ (M=Mo, W;X=S, Se) have been widely investigated for potential applications in optoelectronics and nanoelectronics. Recently, alloybased monolayers of TMDCs have provided a stable and versatile technique to tune the physical properties and optimize them for potential applications. Here, we present experimental evidence for the existence of an intermediate alloy state between the MoSe₂-like and the WSe₂-like behavior of the neutral exciton (X₀) using temperature-dependent photoluminescence (PL) of the monolayer Mo_xW_1–xSe₂ alloy. The existence of a maximum PL intensity around 120 Kcan be explained by the competition between the thermally activated bright states and the non-radiative quenching of the bright states. Moreover, we also measured localized exciton (X_B) PL peak in the alloy and the observed behavior agrees well with a model previously proposed for the 3D case, which indicates the theory also applies to 2D systems. Our results not only shed light on bright–dark states and localized exciton physics of 2D semiconductors, but also offer a new route toward the control of the bright–dark transition and tailoring optical properties of 2D semiconductors through defect engineering.

Keywords: TMDCs, alloy, excitons, localized states, bright–dark states