Excitonic luminescence of WSe₂ bilayer

WSe₂ films with a thickness of two monolayers were obtained on Si/SiO₂ substrates by top-down technique. The thickness and composition of the films are confirmed by measurements of Raman spectra, photoluminescence and interference contrast in three colors (RGB channels). The luminescence of WSe₂ bilayers was studied at the liquid helium temperature (5 K). It is shown that, at low temperatures, the fine structure of the emission spectrum near the direct edge of intrinsic absorption is determined by recombination of A-excitons in the ground or excited state, as well as various complexes (trions and excitons, bound on defects) with their participation. The emission spectrum near the indirect fundamental absorption edge is described in terms of exciton luminescence processes in which the energy and momentum of an exciton are transmitted to phonons, corresponding to the Λ-point of the Brillouin zone. A possible contribution of the electron-hole liquid to the emission spectrum is discussed.

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