Tunable Exciton Radiative Recombination Lifetime in Twisted Bilayer Molybdenum Disulfide

Abstract

The ability to control exciton radiative recombination dynamics is a promising element for expanding applications of atomically thin two-dimensional (2D) materials. Here, we show that twist angle can be used to control the interlayer indirect exciton dynamics of transitionmetal dichalcogenide bilayers by changing the indirect band gaps in the two layers. Exciton radiative recombination lifetimes of twisted MoS 2 bilayers are monitored by fluorescence lifetime imaging microscopy (FLIM) technology. Interestingly, interlayer twists cause only a weak change of direct excitons, but greatly modify the indirect exciton recombination channel due to the repulsive steric effects. Thus, the indirect exciton radiative recombination lifetime first increases from 5.2 to 27.0 ns with twist angle (θ) changing from 0 to 30°(more than 5-fold), and then decreases to 8.3 ns with θ further increasing to 60°. Our work paves a new route for engineering exciton radiative recombination dynamics of 2D materials, which can improve the future applications of optoelectronic devices based on 2D materials.

Twist-Dependent Tuning of Excitonic Emissions in Bilayer WSe2

“…Contradictorily, in the literature, several earlier works have reported a blue shift in PL with increasing t-angles in BL WSe 2 . 45,4645,46 But these studies carried out at cryogenic temperatures (<10 K) are for momentum indirect Q−K or Q−Γ emissions at lower energies (∼1.5−1.6 eV). As opposed to Mo-based TMDs, 47−49 the direct emission peak near ∼1.7 eV in WSe 2 is strongly quenched at lower temperatures due to the presence of lowerlying dark exciton states (see Supporting Information, Figure S5).…”

Ultrafast charge transfer and carrier dynamics in a WS2/MoSe2 few-layer van der Waals heterostructure

“…In both cases, the recombination lifetimes are limited by the nonradiative recombination, since the radiative recombination lifetime of such indirect excitons is expected to be several nanoseconds. 56 The difference between the two lifetimes could reflect their different crystalline qualities (defect density). In the heterostructure, the T valleys of both layers are occupied by the electrons after the interlayer CT process, while the holes populate the Γ valley of MoSe 2 .…”

Structure modulation of two-dimensional transition metal chalcogenides: recent advances in methodology, mechanism and applications

“…The bandgaps of few-layer semiconducting twisted H-phase TMDs vary due to the band valleys located in different symmetric sites of their Brillouin zones. [226][227][228] Fig. 21(a) shows the band structures of monolayer and bilayer MoS 2 with different twist angles as an example.…”