Identifying Defect-Induced Trion in Monolayer WS₂ via Carrier Screening Engineering

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Monolayer transition-metal dichalcogenides exhibit high exciton binding energies (BEs) enabling exotic many-body effects.
• Defect-induced trions and their binding energies, crucial for understanding charge screening, have not been previously observed.

Purpose of the Study:

• To investigate and report the observation of defect-induced A-trions and B-trions in monolayer tungsten disulfide (WS2).
• To explore the role of carrier screening engineering in modulating these defect-induced excitonic states.
• To determine the binding energies of defect-induced trions and compare them with other excitonic states.

Main Methods:

• Carrier screening engineering using photogenerated carrier modulation, external doping (rhenium), and substrate scattering.
• Utilized a trap-free hexagonal boron nitride substrate to confirm the absence of defect-induced trion peaks.
• Employed spatial binding energy mapping to demonstrate defect-induced trion localization.

Main Results:

• Successfully observed defect-induced A-trions and B-trions in monolayer WS2, strongly coupled with SiO2 hole traps.
• Defect-induced trions were more prominent in rhenium-doped WS2 and absent on hexagonal boron nitride substrates.
• The defect-induced A-trion state exhibited the highest binding energy (~214 meV), surpassing neutral excitons and trions.

Conclusions:

• This study demonstrates the existence and characterization of defect-induced trions in monolayer WS2.
• Carrier screening engineering is a viable method to tune and study these excitonic states.
• The findings open avenues for exploring novel many-body physics and potential applications in 2D materials.