Efficient cathodoluminescence of monolayer transitional metal dichalcogenides in a van der Waals heterostructure

TL;DR

This study demonstrates a significant enhancement in cathodoluminescence of monolayer transition metal dichalcogenides within van der Waals heterostructures, enabling new opto-electronic applications.

Contribution

First demonstration of efficient cathodoluminescence in monolayer TMDs using hBN encapsulation within heterostructures.

Findings

Cathodoluminescence intensity increases over 1000-fold with optimized heterostructure design.

Emission properties depend strongly on the thickness of surrounding layers.

Strain-induced exciton peak shifts are observed in suspended heterostructures.

Abstract

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 opto-electronic applications including solar cells, photo-detectors, light-emitting diodes and photo-transistors, 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 1000 folds. 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.