Nano Lett. http://doi.org/bckx (2016)

Similar to the spins of electrons and holes, valleys present in the electronic band structure of some materials could potentially be used to process data. In the development of such valleytronic devices, monolayer transition metal dichalcogenides are of particular interest because of their inherent spin–valley coupling. Wei Huang, Ting Yu and colleagues have now shown that the circularly polarized light emission from valleys in transition metal dichalcogenides in a light-emitting diode (LED) can be manipulated by electrical tuning.

The researchers — who are based at Nanjing Tech University, Nanyang Technological University, Nanjing University of Posts and Telecommunications and the National University of Singapore — created a p–i–n heterostructure from monolayer WS2. Unlike conventional approaches, where the control of the valley degree of freedom is achieved through an external magnetic field or a polarized laser light, the circularly polarized electroluminescence in this valley-LED was induced by an applied forward bias. Notably, the experimental data showed a strong correlation between the degree of circular polarization and the injection current. Although the emission mechanism was different from that of a typical LED, this valley-based optoelectronic device exhibited excellent diode-like behaviour in addition to its unique electroluminescence response, which was characterized by a tunable polarization and intensity.