Observation of Long-Lived Interlayer Excitons in Monolayer MoSe2-WSe2 Heterostructures

Abstract

Two-dimensional (2D) materials, such as graphene1, boron nitride2, and transition metal dichalcogenides (TMDs)3-5, have sparked wide interest in both device physics and technological applications at the atomic monolayer limit. These 2D monolayers can be stacked together with precise control to form novel van der Waals heterostructures for new functionalities2,6-9. One highly coveted but yet to be realized heterostructure is that of differing monolayer TMDs with type II band alignment10-12. Their application potential hinges on the fabrication, understanding, and control of bonded monolayers, with bound electrons and holes localized in individual monolayers, i.e. interlayer excitons. Here, we report the first observation of interlayer excitons in monolayer MoSe2-WSe2 heterostructures by both photoluminescence and photoluminescence excitation spectroscopy. The energy and luminescence intensity of interlayer excitons are highly tunable by an applied vertical gate voltage, implying electrical control of the heterojunction band-alignment. Using time resolved photoluminescence, we find that the interlayer exciton is long-lived with a lifetime of about 1.8 ns, an order of magnitude longer than intralayer excitons13-16. Our work demonstrates the ability to optically pump interlayer electric polarization and provokes the immediate exploration of interlayer excitons for condensation phenomena, as well as new applications in 2D light-emitting diodes, lasers, and photovoltaic devices.

With Supplementary Materials

References in corpus (8)

• Electric Field Effect in Atomically Thin Carbon Films
• Two Dimensional Atomic Crystals
• Boron nitride substrates for high-quality graphene electronics
• Valley polarization in MoS2 monolayers by optical pumping
• Atomically thin p-n junctions with van der Waals heterointerfaces
• Ultrafast Charge Transfer in Atomically Thin MoS2/WS2 Heterostructures
• Strong interlayer coupling in van der Waals heterostructures built from single-layer chalcogenides
• High-temperature superfluidity with indirect excitons in van der Waals heterostructures

Cited by in corpus (5)

• Light-emitting diodes by bandstructure engineering in van der Waals heterostructures
• Determination of band alignment in the single layer MoS2/WSe2 heterojunction
• Efficient Interlayer Relaxation and Transition of Excitons in Epitaxial and Non-epitaxial MoS2/WS2 Heterostructures
• Observation of interlayer phonon modes in van der Waals heterostructures
• Lateral heterojunctions within monolayer semiconductors