Substitutional and Adsorptive Defects Induce Local Bandgap Modulation and Defect Emission in Monolayer MoS₂

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Defect-related photoluminescence (PL) in monolayer molybdenum disulfide (MoS2) is crucial for its optoelectronic applications.
• The microscopic origins of multiple emission components in MoS2 PL have remained controversial, often attributed solely to sulfur vacancies.

Purpose of the Study:

• To elucidate the microscopic origins of defect-related emissions in monolayer MoS2.
• To differentiate between adsorptive and substitutional defect contributions to photoluminescence.
• To investigate the role of oxygen chemistry in defect formation and luminescence.

Main Methods:

• Low-temperature photoluminescence (PL) spectroscopy of monolayer MoS2.
• Laser exposure experiments to probe the stability of defect emissions.
• Ion irradiation (O, Si, Cl) to induce and study specific defects.

Main Results:

• Three distinct defect-related emissions (D1-D3) were observed beyond the neutral exciton peak.
• Emissions D2 and D3 were quenched by laser exposure, indicating adsorptive origins.
• Stable D1 emission and the reproduction of all three emissions after oxygen ion irradiation confirmed oxygen-related substitutional defects.
• Oxygen substitution was shown to narrow the bandgap and facilitate exciton funneling.

Conclusions:

• A unified understanding of substitutional and adsorptive defect luminescence in MoS2 is provided.
• Oxygen substitution is identified as a key factor in defect luminescence and bandgap modification.
• Oxygen chemistry plays a critical role in tuning excitonic behavior in 2D semiconductors.