Ultrafast Charge-Transfer Dynamics in Twisted MoS₂/WSe₂ Heterostructures

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Two-dimensional transition metal dichalcogenides (TMDs) are key for van der Waals heterojunctions.
• Type-II band alignment in TMDs enables efficient charge separation.
• Crystallographic alignment influences heterostructure properties for optoelectronics and valleytronics.

Purpose of the Study:

• Investigate ultrafast charge-transfer dynamics in MoS2/WSe2 heterostructures.
• Understand the influence of stacking angles on charge transfer.
• Elucidate the role of different excitation energies on charge transfer mechanisms.

Main Methods:

• Utilized time- and polarization-resolved second-harmonic imaging microscopy.
• Achieved an unprecedented temporal resolution of approximately 10 femtoseconds.
• Studied three MoS2/WSe2 heterostructures with varying stacking angles.

Main Results:

• Observed electron transfer from WSe2 to MoS2, with transfer times as short as 12 fs at 1.70 eV excitation.
• Demonstrated significant dependence of electron transfer on stacking angle.
• Identified ultrafast hole transfer at 1.85 eV excitation, with minor stacking-angle dependence, suggesting dominant radiative recombination of indirect excitons.

Conclusions:

• Stacking angle critically influences ultrafast electron transfer dynamics in MoS2/WSe2 heterostructures.
• Hole transfer dynamics are less sensitive to stacking angles, with exciton recombination being a key decay pathway.
• Findings provide crucial insights for designing high-performance optoelectronic and valleytronic devices based on TMD heterostructures.