Exciton Radiative Lifetime in Transition Metal Dichalcogenide Monolayers

• Published in: arXiv.org 2016-03
• Main Authors: Robert, C, Lagarde, D, Cadiz, F, Wang, G, Lassagne, B, Amand, T, Balocchi, A, Renucci, P, Tongay, S, Urbaszek, B, Marie, X
• Format: Article
• Language: English
• Subjects: Chalcogenides; Decay; Excitons; Monolayers; Photoluminescence; Radiative lifetime; Radiative recombination; Temperature dependence; Thermodynamic equilibrium; Transition metal compounds
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1603.00277

We have investigated the exciton dynamics in transition metal dichalcogenide mono-layers using time-resolved photoluminescence experiments performed with optimized time-resolution. For MoSe2 monolayers, we measure \(\tau_{rad}=1.8\pm0.2\) ps that we interpret as the intrinsic radiative recombination time. Similar values are found for WSe2 mono-layers. Our detailed analysis suggests the following scenario: at low temperature (T \(\leq\) 50 K), the exciton oscillator strength is so large that the entire light can be emitted before the time required for the establishment of a thermalized exciton distribution. For higher lattice temperatures, the photoluminescence dynamics is characterized by two regimes with very different characteristic times. First the PL intensity drops drastically with a decay time in the range of the picosecond driven by the escape of excitons from the radiative window due to exciton- phonon interactions. Following this first non-thermal regime, a thermalized exciton population is established gradually yielding longer photoluminescence decay times in the nanosecond range. Both the exciton effective radiative recombination and non-radiative recombination channels including exciton-exciton annihilation control the latter. Finally the temperature dependence of the measured exciton and trion dynamics indicates that the two populations are not in thermodynamical equilibrium.