Fundamental limits of exciton-exciton annihilation for light emission in transition metal dichalcogenide monolayers

Abstract

We quantitatively illustrate the fundamental limit that exciton-exciton annihilation (EEA) may impose to the light emission of monolayer transition metal dichalcogenide (TMDC) materials.The EEA in TMDC monolayers shows dependence on the interaction with substrates as its rate increases from 0.1 cm 2 /s (0.05 cm 2 /s) to 0.3 cm 2 /s (0.1 cm 2 /s) with the substrates removed for WS 2 (MoS 2 ) monolayers. It turns to be the major pathway of exciton decay and dominates the luminescence efficiency when the exciton density is beyond 10 10 cm -2 in suspended monolayers or 10 11 cm -2 in supported monolayers. This sets an upper limit on the density of injected charges in light emission devices for the realization of optimal luminescence efficiency. The strong EEA rate also dictates the pumping threshold for population inversion in the monolayers to be 12-18 MW/cm 2 (optically) or 2.5-4×10 5 A/cm 2 (electrically).

Onset of exciton-exciton annihilation in single-layer black phosphorus

“…We rule out the contribution related to the formation of biexcitonic complexes, which might possibly be responsible for an increasing fast decay component, as no additional low energy peaks corresponding to biexcitonic recombination are observed at high power [28]. Instead, we propose exciton-exciton annihilation, already observed in TMDs [14][15][16][17][18], as the recombination mechanism responsible for the observed nonlinear exciton dynamics. In this framework, the rate equation for the exciton population n(t) can be written:…”

“…Considering that the band gap of black phosphorus (and hence its emission energy) is known to blueshift with increasing temperature [28,38,39], we can rule out laser-induced heating effects even at the highest excitation intensity, as no shift of the PL emission energy is observed for this sample. This, along with the constant line shape [28] (pointing to the absence of biexciton recombination), the saturation of the PL intensity at high excitation power, and the 2D excitonic character of the emission of black phosphorus, suggests that other nonlinear processes, namely exciton-exciton annihilation, play an important role [13][14][15][16][17][18].…”

“…In particular, exciton-exciton annihilation is a scattering mechanism in which one exciton recombines nonradiatively, transferring its energy and momentum to another exciton, which subsequently relaxes to lower energy states, losing the energy initially gained, through electron-phonon interactions. This process, which can be viewed as the exciton counterpart of Auger recombination for free carriers, has been demonstrated to be a very efficient nonradiative recombination channel (particularly at high injection levels) in low-dimensional systems such as carbon nanotubes [5][6][7][8], graphene nanoribbons [9], colloidal quantum dots and nanorods [10,11], organic semiconductors [12,13], and monolayer transition metals dichalcogenides (TMDs) [14][15][16][17][18]. Other than the understanding of fundamental exciton dynamics, the interest of exciton-exciton annihilation resides in its significant technological impact, since it provides an upper limit for the carrier density under different excitation conditions.…”

Influence of the substrate material on the optical properties of tungsten diselenide monolayers

“…For a practical device, MLs on substrates with small annihilation rates can be used at high pump rates until excitonexciton annihilation becomes dominant [82].…”

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

“…The first member of the transition metal dichalcogenides (TMDC) to be established as a direct gap semiconductor in monolayer (ML) form was MoS 2 [1,2], which has resulted in a global research effort exploring this promising 2D semiconductor family [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. First prototype device applications, such as transistors [17][18][19] and light emitters [20][21][22], have shown the promise of this atomically thin material for electronics and optoelectronics.…”