Electrical Modulation of Exciton Complexes in Light-Emitting Tunnel Transistors of a van der Waals Heterostructure

Transition metal dichalcogenides (TMDs) and their van der Waals heterostructures provide a unique platform for optoelectronic applications. The strong Coulomb interaction in TMDs creates various tightly bound electron-hole combinations, resulting in various exciton complexes. Despite the great potential of exciton complexes in optoelectronics, most related studies have been performed using optical excitation methods at low temperatures. Here, we demonstrate the electrical modulation of exciton complexes in light-emitting tunnel transistors (LETTs) of van der Waals heterostructures with tunnel junctions of monolayer WSe2 sandwiched by tunnel barriers of hexagonal boron nitride (hBN) and graphene electrodes. Electrons and holes were electrically driven into the monolayer WSe2 by tunneling through hBN, leading to strong electroluminescence (EL) via recombination. To electrically control the exciton complexes by varying the charge balance, we constructed an additional electrode (control electrode) in direct contact with WSe2. We substantially modulated the Fermi energy of WSe2 by direct injection or extraction of electrons from the control electrode, allowing for the modulation of exciton complexes such as excitons, trions, and exciton-polarons, in strong room-temperature EL. This work provides a novel way to electrically stabilize exciton complexes in light-emitting devices of van der Waals heterostructures, which is beneficial for electrically driven excitonic devices.