Portal de Periódicos da CAPES

Exciton radiative lifetime in transition metal dichalcogenide monolayers

2016; American Physical Society; Volume: 93; Issue: 20 Linguagem: Inglês

10.1103/physrevb.93.205423

2469-9977

C. Robert, Delphine Lagarde, Fabian Cadiz, Gang Wang, B. Lassagne, T. Amand, A. Balocchi, P. Renucci, Sefaattin Tongay, B. Urbaszek, X. Marie,

MXene and MAX Phase Materials

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.