Electric-field-induced strong enhancement of electroluminescence in multilayer molybdenum disulfide

The layered transition metal dichalcogenides have attracted considerable interest for their unique electronic and optical properties. While the monolayer MoS 2 exhibits a direct bandgap, the multilayer MoS 2 is an indirect bandgap semiconductor and generally optically inactive. Here we report electric-field-induced strong electroluminescence in multilayer MoS 2. We show that GaN-Al 2 O 3 -MoS 2 and GaN-Al 2 O 3 -MoS 2 -Al 2 O 3 -graphene vertical heterojunctions can be created with excellent rectification behaviour. Electroluminescence studies demonstrate prominent direct bandgap excitonic emission in multilayer MoS 2 over the entire vertical junction area. Importantly, the electroluminescence efficiency observed in multilayer MoS 2 is comparable to or higher than that in monolayers. This strong electroluminescence can be attributed to electric-field-induced carrier redistribution from the lowest energy points (indirect bandgap) to higher energy points (direct bandgap) in k-space. The electric-field-induced electroluminescence is general for other layered materials including WSe 2 and can open up a new pathway towards transition metal dichalcogenide-based optoelectronic devices.