Quantum Confined Luminescence in Two Dimensions

The field of nanophotonics has witnessed a surge of interest in localized light emitters, driven by their potential to revolutionize optoelectronic devices. These emitters, including nanoparticles, nanowires, and quantum wells, confine electrons, holes or excitons to nanoscale dimensions, leading to unique emission characteristics and potential applications in quantum technologies. This study explores a new type of localized emitter: two-dimensional quantum dots formed in monolayers of the transition metal dichalcogenides (TMD) MoSe₂, and WSe₂. By selectively growing nanometric islands of MoSe₂,surrounded by WSe₂, we achieve quantum confinement in islands with sizes approaching the materials’ exciton Bohr radii. The type-II band alignment between these materials localizes electrons in the MoSe₂, and holes in the WSe₂, barriers, leading to emission below the band gap of MoSe₂, even when electrons are confined. Individual 2D dots were probed using cathodoluminescence in a scanning transmission electron microscope. These findings pave the way for the design of more compact optoelectronic devices, such as miniaturized lasers and LEDs.