In-plane and out-of-plane domain orientation dispersions in 1 to 3 monolayers epitaxial WS2 and MoS2 films on GaN(0001) film/sapphire(0001)

Transition-metal dichalcogenides and their heterostructures have attractive potential applications in electronics and optoelectronics. Wafer scale 1 to 3 monolayers WS2 and MoS2 ultrathin films on GaN/sapphire substrates were grown by metal organic chemical vapor deposition. Azimuthal reflection high-energy electron diffraction (ARHEED) was used to characterize the long-range order of these TMDC ultrathin films. The RHEED patterns of WS2 and MoS2 show stripes and arcs but the MoS2 on GaN shows sharp spots in addition to stripes and arcs. The 2D map constructed from ARHEED patterns shows that WS2 is epitaxial and has an in-plane domain orientation dispersion. For the MoS2 on GaN/sapphire substrate, the 2D map shows concentric continuous rings for each diffraction order of MoS2 and GaN indicating that the in-plane MoS2 domain orientation and GaN nanocrystals are random. The out-of-plane orientation dispersion of MoS2 on the GaN substrate is larger than that of WS2 on the GaN substrate. The observations of stripes, arcs, and spots from RHEED patterns and the 2D maps reveal the deviation of ultrathin epitaxial films from its perfect epitaxy, especially the TMDC domain orientation dispersion over a large area. These rich findings from 2D maps broaden the application of ARHEED in more than one monolayer thick 2D materials. [Display omitted] •Azimuthal RHEED characterization of wafer scale epitaxial ultrathin WS2 on GaN and MoS2 on GaN.•RHEED patterns of 1–3 monolayers WS2 show stripes and arcs.•RHEED patterns of 1–3 monolayers MoS2 show sharp spots in addition to stripes and arcs.•RHEED patterns of WS2 and MoS2 show out-of-plane angular dispersions.•2D map of WS2 on GaN shows in-plane angular dispersion of WS2 domains.•2D map of MoS2 on GaN shows random MoS2 domains and GaN nanocrystals.