Dilute Acceptor-bound Excitons in a Monolayer Semiconductor

Abstract Atomic defects in two-dimensional (2D) semiconductors are promising single exciton traps for achieving quantum emission. However, excessively high density of defects often makes it impractical to optically address the quantum nature of such quasi-particles, preventing strategic exciton engineering. Here, we report a versatile strategy for dilute acceptor impurity doping of monolayer WS2, which enables the study of isolated bound excitons. We observe two distinct types of acceptor-bound excitons: one of them is characterized by a large binding energy, allowing its observation at room temperature and the other by an extremely narrow linewidth (< 1 meV), showing strong resemblance to quantum emitters in WSe2. Polarization-resolved spectroscopy and magnetic field dependence reveal their strong contribution of free exciton character. In particular, the latter type exhibits characteristics of acceptor-bound dark excitons. Our work demonstrates dilute impurity doping as a promising strategy towards optically addressable quantum states in monolayer semiconductors.