Photoluminescence Studies of Excitonic Complexes in Atomically Thin Mo(SySe1-y)2 Alloys

J. Jadczak Department of Experimental Physics, Wrocław University of Science and Technology, Wrocław, Poland

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Transition metal dichalcogenides show new emergent properties at monolayer thickness, notably strong Coulomb and electron-phonon interactions enable new insight into physics of many body effects. Here, we report photoluminescence and reflectivity contrast measurements of excitons (X) and trions (T) and the Raman spectra of phonons in monolayers of Mo(SySe1-y)2 alloys with sulfur mole content from y=0 up to y=1. Binary MoSe2 and ternary Mo(SySe2-y) alloys exhibit contrasting behavior in the temperature evolution of excitons and trions photoluminescence intensity from T=7-295 K. In MoSe2 a trion dominates photoluminescence spectra at low temperatures but exciton dominates photoluminescence at higher temperature. In contrast, in ternary Mo(SySe1-y)2 alloys and MoS2 trions dominate photoluminescence spectra at all measured temperatures, with the trion to exciton photoluminescence intensity ratio increasing with sulfur content. We attribute the strong increase of the trion photoluminescence intensity in Mo(SySe1-y)2 monolayers with increase of sulfur mole content to the significant increase of the two-dimensional electron gas concentration and also to the strong exciton-trion coupling mediated by an optical phonon. We also demonstrate that increasing sulfur content in Mo(SySe1-y)2 alloys stabilizes total photoluminescence intensity at high temperature.

DOI: 10.12693/APhysPolA.132.307 topics: Transition metal dichalcogenides monolayers, exciton, trion, phonon