Paramagnetic Intrinsic Defects in Polycrystalline Large-Area 2D MoS₂ Films Grown on SiO₂ by Mo Sulfurization

Area of Science:

• Materials Science
• Condensed Matter Physics
• 2D Materials

Background:

• Molybdenum disulfide (MoS2) is a promising two-dimensional material with applications in electronics.
• Point defects and grain boundaries are known to degrade carrier mobility in MoS2 films.
• Understanding these defects is crucial for optimizing MoS2-based devices.

Purpose of the Study:

• To identify and characterize atomic-scale defects in polycrystalline 2H MoS2 films.
• To investigate the correlation between defects and carrier mobility degradation.
• To determine the nature and origin of a previously unreported anisotropic defect.

Main Methods:

• Low-temperature electron spin resonance (ESR) spectroscopy was employed.
• High-purity, large-area, few-monolayer (ML) 2H MoS2 films synthesized by sulfurization of Mo layers were studied.
• Analysis of ESR signal features and correlation with film properties (e.g., grain size) were performed.

Main Results:

• A previously unreported anisotropic defect with axial symmetry was detected.
• The defect exhibits specific g-values (g_// = 2.00145, g_⊥ = 2.0027) and a density of ~3 × 10^12 cm^-2 for a 4 ML film.
• Defect density inversely correlates with grain size, suggesting a domain boundary origin.
• The defect is tentatively identified as an antisite defect involving sulfur substituting molybdenum (S or S2 on Mo site).

Conclusions:

• Grain boundaries in MoS2 films act as significant sources of mobility-degrading defects.
• The identified antisite defect poses a major challenge for carrier mobility and overall layer functionality.
• Further research is needed to mitigate these defects for advanced MoS2 applications.