Monolayer transition-metal dichalcogenides (TMDs) exhibit exceptional optical properties useful for optoelectronic applications. However, for industrial use, a large-scale homogeneity optical response is needed. To address this demand we utilize molecular beam epitaxy (MBE). In our previous works, we have achieved high optical quality of MBE-grown MoSe2 on exfoliated [1,2] and large-scale epitaxial [3] hexagonal boron nitride (hBN) and we have mixed MoSe2 with Mn ions and showed that it can lead to the induction of 1T’ phase of this material [4]. Here, we report on the WSe2 grown on hBN by MBE, demonstrating high structural and optical quality. For the first time, multi-particle excitonic systems can be observed in WSe2 samples fabricated in a bottom-up approach, without mechanical transfer. WSe2 was investigated by atomic force microscopy and transmission electron microscopy in cross-section to verify their structural properties. Both techniques confirm that most of the TMD material is observed in the form of one monolayer thin flakes, that covers ~50% of the substrate surface. Both techniques confirm the hexagonal structure of the material as well as high crystalline quality. Low-temperature photoluminescence, reflectivity, and PLE measurements reveal narrow and resolved spectral lines of neutral and charged exciton as well as a wide range of localized excitons present in energies lower than charged exciton. The material exhibits high homogeneity of optical properties within hBN terraces used as a substrate.
[1] W. Pacuski et al., Nano Letters 20, 3058 (2020).
[2] M. Raczyński et al., ArXiv:2502.17314 (2025).
[3] K. Ludwiczak et al., ACS Appl. Mater. Interfaces 16, 49701(2024).
[4] J. Kucharek, R. Bożek, W. Pacuski, Mater. Sci. Semicond. Process. 163, 107550 (2023).