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Monolayer two-dimensional transitional metal dichalcogenides, such as MoS2, WS2, and WSe2, are direct band gap semiconductors with large exciton binding energy. They attract growing attentions for optoelectronic applications including solar cells, photodetectors, light-emitting diodes and phototransistors, capacitive energy storage, photodynamic cancer therapy, and sensing on flexible platforms. While light-induced luminescence has been widely studied, luminescence induced by injection of free electrons could promise another important applications of these new materials. However, cathodoluminescence is inefficient due to the low cross-section of the electron-hole creating process in the monolayers. Here for the first time we show that cathodoluminescence of monolayer chalcogenide semiconductors can be evidently observed in a van der Waals heterostructure when the monolayer semiconductor is sandwiched between layers of hexagonal boron nitride (hBN) with higher energy gap. The emission intensity shows a strong dependence on the thicknesses of surrounding layers and the enhancement factor is more than 500-fold. Strain-induced exciton peak shift in the suspended heterostructure is also investigated by the cathodoluminescence spectroscopy. Our results demonstrate that MoS2, WS2, and WSe2 could be promising cathodoluminescent materials for applications in single-photon emitters, high-energy particle detectors, transmission electron microscope displays, surface-conduction electron-emitter, and field emission display technologies. [ABSTRACT FROM AUTHOR]

Axially stacked quantum dots (QDs) in nanowires (NWs) have important applications in nanoscale quantum devices and lasers. However, there is lack of study of defect-free growth and structure optimization using the Au-free growth mode. We report a detailed study of self-catalyzed GaAsP NWs containing defect-free axial GaAs QDs (NWQDs). Sharp interfaces (1.8-3.6 nm) allow closely stack QDs with very similar structural properties. High structural quality is maintained when up to 50 GaAs QDs are placed in a single NW. The QDs maintain an emission line width of <10 meV at 140 K (comparable to the best III-V QDs, including nitrides) after having been stored in an ambient atmosphere for over 6 months and exhibit deep carrier confinement (∼90 meV) and the largest reported exciton-biexciton splitting (∼11 meV) for non-nitride III-V NWQDs. Our study provides a solid foundation to build high-performance axially stacked NWQD devices that are compatible with CMOS technologies.

Monolayer two-dimensional transitional metal dichalcogenides, such as MoS 2 , WS 2 , and WSe 2 , are direct band gap semiconductors with large exciton binding energy. They attract growing attentions for optoelectronic applications including solar cells, photodetectors, light-emitting diodes and phototransistors, capacitive energy storage, photodynamic cancer therapy, and sensing on flexible platforms. While light-induced luminescence has been widely studied, luminescence induced by injection of free electrons could promise another important applications of these new materials. However, cathodoluminescence is inefficient due to the low cross-section of the electron-hole creating process in the monolayers. Here for the first time we show that cathodoluminescence of monolayer chalcogenide semiconductors can be evidently observed in a van der Waals heterostructure when the monolayer semiconductor is sandwiched between layers of hexagonal boron nitride (hBN) with higher energy gap. The emission intensity shows a strong dependence on the thicknesses of surrounding layers and the enhancement factor is more than 500-fold. Strain-induced exciton peak shift in the suspended heterostructure is also investigated by the cathodoluminescence spectroscopy. Our results demonstrate that MoS 2 , WS 2 , and WSe 2 could be promising cathodoluminescent materials for applications in single-photon emitters, high-energy particle detectors, transmission electron microscope displays, surface-conduction electron-emitter, and field emission display technologies.