Directly Probing Stacking-Engineered Defect State Delocalization in Marginally Twisted Bilayer WS₂

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Defect states in bilayer transition metal dichalcogenides (TMDs) are crucial for optoelectronic devices.
• Stacking-dependent defect state delocalization affects carrier capture and device performance.
• Top-layer defects mask the observation of delocalized states, while bottom-layer defects are accessible.

Purpose of the Study:

• To distinguish and characterize bottom-layer charged defects in twisted bilayer WS₂.
• To investigate the influence of stacking configurations on defect state delocalization.
• To understand the atomic-scale mechanisms governing defect behavior for improved device engineering.

Main Methods:

• Scanning tunneling microscopy/spectroscopy (STM/STS).
• Image charge analysis.
• Defect state spectroscopy.

Main Results:

• Bottom-layer W-aligned defects exhibit weaker charge screening and stronger interlayer orbital coupling.
• These defects show enhanced carrier accumulation and out-of-plane state propagation.
• W-aligned defects display pronounced delocalization and large carrier capture cross-sections, detrimental to device performance.

Conclusions:

• Atomic-scale mechanisms of defect state delocalization in bilayer TMDs elucidated.
• W-aligned defects are identified as key contributors to unfavorable electronic properties.
• Findings provide fundamental insights for defect engineering in TMD-based quantum devices.