Exciton Luminescence of Wse2 Bilayers

WSe2 films with thickness of two monolayers are deposited on SiO2/Si substrates using the top-down technology. The thickness and the composition of the films are confirmed by measurements of the Raman spectra, photoluminescence, and interference contrast in three RGB channels. The luminescence of WSe2 bilayers is studied at temperatures decreased down to 5 K. It is shown that at low temperatures, the fine structure of the emission spectrum near the direct intrinsic absorption edge is determined by the recombination of A excitons (in the ground or excited state) and various complexes (trions and excitons bound on defects). The emission spectrum near the indirect fundamental absorption edge is described by exciton luminescence processes in which the exciton energy and momentum are transferred 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.