Directly Probing Stacking‐Engineered Defect State Delocalization in Marginally Twisted Bilayer WS 2
Yi‐Feng Chen, Hung‐Chang Hsu, Jyun‐Yi He, Hao‐Yu Chen, Yan‐Ruei Lin, Ming‐Yang Li, Iuliana P. Radu, Ya‐Ping ChiuABSTRACT
Defect states in bilayer transition metal dichalcogenides (TMDs) represent a promising platform for optoelectronic devices, where stacking‐dependent defect state delocalization influences the carrier capturing probability and device performance. However, top‐layer defects dominate the electronic measurement and obscure the observation of delocalized defect states, whereas only bottom‐layer defects allow direct observation of defect state delocalization at the surface. Here, we employ scanning tunneling microscopy/spectroscopy and image charge analysis to distinguish bottom‐layer charged defects across distinct stacking configurations in lattice‐reconstructed twisted bilayer WS 2 . Our results reveal that defects aligned with W atoms exhibit weaker charge screening and stronger interlayer orbital coupling, resulting in enhanced carrier accumulation and out‐of‐plane state propagation. Defect state spectroscopy demonstrates that W‐aligned defects show pronounced delocalization and the largest carrier capture cross‐section, which is unfavorable for optoelectronic and electronic devices. Our findings elucidate the atomic‐scale mechanisms governing defect state delocalization in bilayer structures, providing fundamental insights for defect engineering in TMD‐based quantum devices.