Observation of long-lived interlayer excitons in monolayer MoSe2–WSe2 heterostructures

TLDR

Van der Waals heterostructures of two‑dimensional materials, including transition metal dichalcogenides, are of great interest for device physics, and type‑II band‑aligned monolayer pairs host interlayer excitons with electrons and holes in separate layers. The study reports the observation of interlayer excitons in monolayer MoSe₂–WSe₂ heterostructures using photoluminescence and photoluminescence excitation spectroscopy. The authors employed photoluminescence and photoluminescence excitation spectroscopy to detect and characterize the interlayer excitons. They found that the interlayer exciton energy and luminescence intensity are tunable by a vertical gate voltage, the lifetime is ~1.8 ns—an order of magnitude longer than intralayer excitons—and optical pumping induces interlayer electric polarization, suggesting prospects for exciton condensation and 2D optoelectronic devices.

Abstract

Van der Waals bound heterostructures constructed with two-dimensional materials, such as graphene, boron nitride and transition metal dichalcogenides, have sparked wide interest in device physics and technologies at the two-dimensional limit. One highly coveted heterostructure is that of differing monolayer transition metal dichalcogenides with type-II band alignment, with bound electrons and holes localized in individual monolayers, that is, interlayer excitons. Here, we report the observation of interlayer excitons in monolayer MoSe2-WSe2 heterostructures by photoluminescence and photoluminescence excitation spectroscopy. We find that their energy and luminescence intensity are highly tunable by an applied vertical gate voltage. Moreover, we measure an interlayer exciton lifetime of ~1.8 ns, an order of magnitude longer than intralayer excitons in monolayers. Our work demonstrates optical pumping of interlayer electric polarization, which may provoke further exploration of interlayer exciton condensation, as well as new applications in two-dimensional lasers, light-emitting diodes and photovoltaic devices.