Development of chemical vapor deposition (CVD) techniques for wafer-scale transition metal dichalcogenides (TMDs) is crucial for their semiconductor applications. Among various CVD precursors, gaseous sources such as WF₆ and H₂S are attractive because of their high controllability and scalability [1]. However, epitaxial growth of crystallographically aligned WS₂ using these precursors remains challenging [2]. Here, we investigated the in-plane orientation of monolayer WS₂ grown on c-plane sapphire using in-plane X-ray diffraction φ-scans. We investigated the growth-time dependence of the WS₂ orientation relative to the sapphire (112̅0) direction (Figs.1,2). At the early stage of growth, the diffraction intensity of the 30°/90° orientation component was dominant. With increasing growth time, the intensity of the 0°/60° component increased, whereas that of the 30°/90° component decreased, resulting in a reversal of their relative intensities. Furthermore, we found that the relative intensities were sensitive to substrate pretreatment and H₂S flow rate. These results suggest that both the substrate condition and chemical environment influence the epitaxial orientation of WS₂, providing a basis for growth with well-defined in-plane orientation.

1. M. Okada, Sci Rep 9, 17678 (2019), DOI:https://doi.org/10.1038/s41598-019-54049-6
2. F. -Z. Chen, Thin Solid Films 792, 140250 (2024), DOI: https://doi.org/10.1016/j.tsf.2024.140250