Reversible Electrical Control of Interfacial Charge Flow across van der Waals Interfaces

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Two-dimensional (2D) materials form van der Waals (vdW) heterostructures with unique properties.
• Controlling photogenerated charge carrier dynamics at vdW interfaces is crucial for optoelectronics.
• Defects are known to influence photoconductive gain but their specific role in interfacial charge dynamics is unclear.

Purpose of the Study:

• Investigate nonequilibrium charge dynamics at the graphene-WS2 vdW interface.
• Elucidate the nature and role of defects in tuning interfacial charge carrier dynamics.
• Explore electrical control over charge separation states and photogating fields.

Main Methods:

• Operando optical-pump terahertz-probe spectroscopy.
• Electrochemical gating of graphene-WS2 vdW heterostructures.
• Analysis of defect occupancy and its effect on charge carrier dynamics.

Main Results:

• Demonstrated full control over charge separation states and photogating field direction.
• Showed that tuning defect occupancy electrically modifies interfacial charge transfer.
• Identified electron occupancy of in-gap states, likely from sulfur vacancies, as key to observed dynamics.

Conclusions:

• Defects, specifically sulfur vacancies in WS2, play a critical role in interfacial charge transfer dynamics.
• Electrochemical gating provides a method to tune defect occupancy and control photogating fields.
• Microscopic insights gained can guide the optimization of 2D material-based optoelectronic devices.