Strong interlayer coupling in van der Waals heterostructures built from single-layer chalcogenides

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Semiconductor heterostructures are crucial for devices like lasers and transistors.
• Transition metal dichalcogenide (TMD) heterostructures offer atomically sharp interfaces and digital control.
• The optoelectronic properties of single-layer TMD heterostructures, particularly optical transition directness, remain unexplored.

Purpose of the Study:

• Investigate the optoelectronic behavior of artificial heterostructures made from single-layer WSe2 and MoS2.
• Determine if optical transitions in these hetero-bilayers are spatially direct or indirect.
• Explore the tunability of interlayer coupling and its impact on optoelectronic properties.

Main Methods:

• Fabrication of artificial heterostructures using single-layer WSe2 and MoS2.
• Photoluminescence and absorption spectroscopy to probe optical transitions.
• Insertion of hexagonal boron nitride (h-BN) dielectric layers to tune interlayer coupling.

Main Results:

• Observed a significant Stokes-like shift (~100 meV) between photoluminescence and absorption peaks.
• Identified a type II band alignment, indicating spatially direct absorption and indirect emission.
• Demonstrated strong photoluminescence intensity from the indirect transition, signifying robust interlayer charge carrier coupling.
• Showcased tunability of this coupling by inserting h-BN dielectric layers.

Conclusions:

• Single-layer TMD hetero-bilayers exhibit strong interlayer coupling with spatially indirect emission.
• This coupling is tunable via dielectric insertions, offering a new avenue for band engineering.
• These findings suggest a new class of semiconductor heterostructures with customizable optoelectronic properties for advanced device applications.