Effect of interface quality on photoluminescence of encapsulated MoSe₂ monolayers

Photoluminescence spectra of excitons and trions in MoSe₂ monolayers encapsulated with hexagonal boron nitride under nonresonant laser excitation were studied. When the size of the laser excitation spot decreases from 8 to 3 nm, individual peaks with a line width of ~2 meV emerge in the photoluminescence spectra, which were unresolved with a larger spot. Studies of the sample surface using a scanning electron microscope revealed the existence of a large number of features at the interfaces of structures with characteristic sizes ranging from submicron to micron and more. It was expected that the lines appearing in the spectrum at small excitation spot sizes were associated with similar submicron inhomogeneities. A study of a specially made heterostructure covered by a metal mask with holes of 1.6 microns in diameter confirmed this assumption.