WSe ₂ Monolayers Grown by Molecular Beam Epitaxy on hBN

A three-step process was developed for growing high-quality, optically uniform WSe₂ monolayers by molecular beam epitaxy (MBE), taking advantage of the use of hexagonal boron nitride (hBN) as a substrate. The process was optimized to maximize the efficiency of photoluminescence and promote the formation of hexagonal WSe₂ domains. Atomic force microscopy was employed to estimate the dispersion of the WSe₂ hexagonal domains' orientation. Monolayer character of the film was identified using optical methods and verified with a high-resolution transmission electron microscopy cross-section. Temperature- and magnetic-field-dependent studies revealed the behavior of exciton complexes to be analogous to that of exfoliated counterparts. Direct growth on hBN, combined with a uniform optical response, proves that MBE-grown WSe₂ is superior to mechanically exfoliated WSe₂ in terms of the convenience of use and reproducibility. The provided results establish significant progress in the optical quality of epitaxially grown transition-metal dichalcogenide monolayers and the fabrication of large-scale functional devices.