Ultrafast Charge Transfer and Recombination Dynamics in Monolayer-Multilayer WSe₂ Junctions Revealed by Time-Resolved...

Area of Science:

• Materials Science
• Condensed Matter Physics
• Physical Chemistry

Background:

• Understanding ultrafast carrier dynamics in junctions of transition metal dichalcogenides (TMDs) is crucial.
• Chemically identical but electronically distinct TMDs present unique interfacial phenomena.
• Monolayer-to-multilayer (1L-ML) WSe2 junctions are common in exfoliated samples.

Purpose of the Study:

• To investigate the ultrafast carrier dynamics at 1L-ML WSe2 junctions.
• To elucidate charge transfer and recombination mechanisms at these interfaces.
• To compare experimental findings with theoretical predictions.

Main Methods:

• Time-resolved photoemission electron microscopy (TR-PEEM) was employed.
• Ab initio quantum dynamics simulations were performed.
• Carrier cooling, exciton-exciton annihilation, and interfacial charge transfer were analyzed.

Main Results:

• Sub-picosecond carrier cooling observed in both 1L- and 7L-WSe2.
• Few-picosecond exciton-exciton annihilation detected on 1L-WSe2.
• Ultrafast interfacial hole transfer from 1L- to 7L-WSe2 on ~0.2 ps timescale.
• Hole recombination across the interface on ~100 ps timescale.
• Hole density accumulation at the 7L-WSe2 interface with a decay length of ~0.60 ± 0.17 μm.

Conclusions:

• Experimental results align with ab initio quantum dynamics.
• Charge transfer occurs from the basal plane to the upper plane of the ML region.
• This distinct charge transfer pathway impacts carrier deactivation in 1L-TMDs adjacent to ML regions.