Title : The origin of point defect formation in epitaxially grown MoS2

The recent breakthrough in wafer-scale single-crystal growth has positioned two-dimensional (2D) semiconducting molybdenum disulfide (MoS₂) as a compelling candidate for beyond-silicon electronics. Nevertheless, the high defect density in epitaxially grown MoS₂ severely hinders its lab-to-fab transition. While the so-called sulfur vacancy (V_S) defects have been extensively studied, here we demonstrate through multiscale simulations that oxygen-for-sulfur substitutions (O_S) constitute the dominant defect species in epitaxially grown MoS₂. Our calculation show that the formation of V_S defects, although thermodynamically possible, is endothermic (3.3 eV) and kinetically very easy to be healed by ambient sulfur. In contrast, the formation of oxygen-for-sulfur substitution (O_S) defects are thermodynamically more favorable (3.9 eV) than V_S defects and kinetically persistent. Simulated scanning tunneling microscopy (STM) images show nearly identical signatures for both defect types, explaining the frequent experimental misidentification of V_S and O_S defects in grown MoS₂. We identify the chemical origin of O_S defects as incomplete sulfurization of oxygen-containing precursors during MoS₂ growth. Based on kinetic Monte Carlo (kMC) simulations, we propose a spatial separation strategy that decouples precursor sulfurization from nucleation zones for complete sulfurization of precursor and intermediate, thereby greatly suppressing the defect formation. Our work fundamentally revises the prevailing V_S-centered understanding of defects in epitaxially grown MoS₂ and provides a practical pathway toward wafer-scale production of low defect density 2D transition metal dichalcogenides.

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