Photoluminescence efficiency of MBE-grown MoSe2 monolayers featuring narrow excitonic lines and diverse grain structures

Recent studies have demonstrated that using hexagonal boron nitride (h-BN) as a substrate for the growth of transition metal dichalcogenides can significantly reduce excitonic linewidths. However, many other optical parameters still require optimization. In this work, we present a detailed study of the low-temperature photoluminescence efficiency of MBE-grown MoSe 2 monolayers on h-BN substrates, comparing them to state-of-the-art exfoliated monolayers encapsulated in h-BN. We demonstrate that a quantitative comparison between samples requires accounting for interference effects and Purcell enhancement or suppression of the emission. By accounting for these effects in both photoluminescence and Raman signals, we show that the overall intrinsic luminescence efficiency is proportional to the sample coverage. Consequently, we find that exciton diffusion and edge effects are not visibly affecting the spectroscopic properties of MBE-grown samples, even for nanometer-sized crystals. • Direct comparison of PL efficiency in MBE-grown and exfoliated MoSe 2 monolayers. • Method corrects for substrate interference including Purcell effect. • PL and Raman brightness scale linearly with monolayer coverage. • Exciton diffusion to grain edges in MBE-grown samples is of small contribution to non-radiative relaxation channel.