Interface engineering of charge-transfer excitons in 2D lateral heterostructures

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• The existence of bound charge transfer (CT) excitons in monolayer lateral heterostructures remains debated.
• Observation of these CT excitons is less confirmed compared to interlayer excitons in vertical heterostructures.

Purpose of the Study:

• To investigate signatures of bound CT excitons in photoluminescence spectra of MoSe2-WSe2 lateral heterostructures.
• To reveal the underlying many-particle processes for CT exciton formation and their tunability.
• To provide a microscopic understanding of optical properties in 2D lateral heterostructures.

Main Methods:

• Microscopic theoretical study based on material-specific theory.
• Photoluminescence (PL) spectroscopy at low temperatures.
• Interface and dielectric engineering for tuning CT exciton properties.

Main Results:

• Predicted the appearance of a low-energy CT exciton for junction widths smaller than the Coulomb-induced Bohr radius.
• Experimental PL measurements confirmed emission in the predicted energy range for bound CT excitons.
• Demonstrated that hBN-encapsulated heterostructures exhibit CT excitons with small binding energies and large dipole moments.

Conclusions:

• This joint theory-experiment study confirms the existence of bound CT excitons in 2D lateral heterostructures.
• CT excitons with small binding energies and large dipole moments are promising for optoelectronics due to efficient exciton dissociation and propagation.
• The findings represent a significant step towards understanding the optical properties of technologically relevant 2D lateral heterostructures.