Monolayer MoS2 and WS2 for Vertical Circular- Polarized-Light-Emitting Diode: from Fundamental Understanding to Device Architecture

Light-emitting diodes (LEDs) have revolutionized lighting and displays due to their numerous advantages over conventional lighting mechanisms. Moreover, the directional nature of luminescent materials has spurred significant advancements in the development of circularly polarized LEDs, which hold transformative potential for applications in biomedical imaging, liquid crystal displays, spintronics, and valleytronics. The performance of circularly polarized LEDs mainly depends on the emitter material, which is this study's focus. In particular, semiconducting-phase 2D monolayer MoS₂ and WS₂ are attractive emitter-material candidates owing to their bandgap versatility, high carrier mobility, high exciton binding energy, polarized-light-emission properties, and unique spin–valley coupling. Several works have examined the fundamental light-emission properties of monolayer MoS₂ and WS₂ from the perspectives of optoelectronic concepts, material fabrication, and device construction. This paper presents approaches to control, tune, and enhance these properties of monolayer MoS₂ and WS₂. Possible guidelines for monolayer-material synthesis (top-down and bottom-up approaches) and device engineering of vertically stacked MoS₂ and WS₂ are presented. Finally, the review considers the material topological characteristics, outlines the challenges and potential of monolayer MoS₂ and WS₂ for developing high-performance commercial circularly polarized LED devices, and proposes a technological roadmap for leveraging other monolayer transition metal dichalcogenide systems in optoelectronic devices.