Epitaxial n-ZnO/MoS2/p-GaN Heterostructure Light-Emitting Diodes.

We investigated an epitaxial strategy for fabricating MoS2 light-emitting diodes (LEDs). A full-coverage MoS2 active layer was grown on p-type GaN, and n-type ZnO nanorods were then vertically aligned on the MoS2 to form a p-n junction with negligible damage to the MoS2. All materials have nearly matched hexagonal structures, enabling single-crystal alignment. Although the continuous MoS2 film formed multiple layers (MLs), the ZnO/MoS2/GaN heterostructure yielded favorable optical characteristics of the ML-MoS2, including internal quantum efficiency comparable to that of the single-layer MoS2. The ZnO/MoS2/GaN LED exhibited stable A and B exciton emissions, which imply direct bandgap transition with spin-orbit coupling. Without mechanically exfoliated or transferred 2D films, this epitaxial approach satisfies the key requirements for fabricating 2D-based optoelectronic and quantum light sources. The strength of epitaxy, such as large-scale scalability and multiple quantum-well formation, will further advance 2D optoelectronics, making them more practical and efficient.