Valley-polarized local excitons in WSe₂/WS₂ vertical heterostructures

Two-dimensional van der Waals heterostructures (vdWHs) are drawing growing interest in the investigation of their valley polarization properties of localized excitons. However, most of the reported vdWHs were made by micro-mechanical peeling, limiting their large-scale production and practical applications. Furthermore, the circular polarization characters of localized excitons in WSe₂/WS₂ heterostructures remain elusive. Here, a bidirectional-flow physical vapor deposition technique was employed for the synthesis of the WSe₂/WS₂ type-II vertical heterostructures. The interfaces of such heterojunctions are sharp and clean, making the neutral excitons of the constituent layers quenched, which significantly highlights the luminescence of the local excitons. The circular polarization of localized excitons in this WSe₂/WS₂ heterostructure was demonstrated by circularly-polarized PL spectroscopy. The degree of the circular polarization of the localized excitons was determined as 7.17% for σ^- detection and 4.78% for σ⁺ detection. Such local excitons play a critical role in a quantum emitter with enhanced spontaneous emission rate that could lead to the evolution of LEDs. Our observations provide valuable information for the exploration of intriguing excitonic physics and the applications of innovative local exciton devices.