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.