Gate-Controlled Ultrafast Interlayer Carrier Flow in Gr/MoS₂ Heterostructures.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Designing next-generation optoelectronic devices requires precise control over carrier transport in heterostructures.
• Van der Waals heterostructures, like molybdenum disulfide (MoS2)/graphene (Gr), offer unique electronic properties for atomically thin optoelectronics.

Purpose of the Study:

• To investigate gate-tunable carrier dynamics in a MoS2/Gr van der Waals heterostructure using ultrafast spectroscopy.
• To understand ultrafast charge transfer processes and their influence on optoelectronic device performance.

Main Methods:

• Fabrication of a transparent field-effect transistor based on a Gr/MoS2 heterostructure.
• Utilized transient terahertz (THz) spectroscopy to probe photoconductivity dynamics in graphene.
• Employed transient absorption spectroscopy to monitor energy state evolution in MoS2.

Main Results:

• Demonstrated gate-tunable THz photoconductivity responses in the Gr/MoS2 heterostructure for both below- and above-bandgap MoS2 excitations.
• Achieved picosecond-scale control over the magnitude and sign of photoconductivity by modulating the graphene Fermi level and defect states.
• Observed tunable photoconductivity responses (positive, negative, or zero) through electrical gating.

Conclusions:

• Provided fundamental insights into carrier dynamics within van der Waals heterostructures.
• Established key design principles for developing advanced optoelectronic devices with tailored performance.
• Highlighted the potential of Gr/MoS2 heterostructures for ultrafast, tunable optoelectronics.