Signatures of self-trapping of trions in monolayer MoS2

Abstract

The peak of the photoluminescence (PL) spectrum associated with the A - trion in monolayer MoS2 on SiO2/Si substrate is typically red shifted in energy relative to its absorption peak by ∼20 meV. Circular polarization anisotropy and pump laser intensity dependence of PL indicates that the A - trion is not localized at a defect. Raman lines in monolayer MoS2 are enhanced and additional lines are seen when the excitation laser has photon energy close to the trion/exciton absorption resonance, indicating their coupling with phonons. Analysis of time resolved PL measurements show that the A - trion emission has a finite rise time of ∼25 ps, unlike the defect bound exciton emission which is also seen. The above characteristics when considered together suggest that trions in monolayer MoS2 could be subject to momentary weak self-trapping through interaction with phonons, a hitherto unexplored property of trions/excitons in two-dimensional transition metal dichalcogenide semiconductors.