Low-temperature annihilation rate for quasilocalized excitons in monolayer MoS2

Abstract

The strong Coulomb forces in monolayer transition metal dichalcogenides ensure that optical excitation of band electrons gives rise to Wannier-Mott excitonic states, each of which can be conceptualized as a composite of a wavepacket corresponding to center-of-mass motion and an orbital state corresponding to the motion of the electron and hole about the center-of-mass. Here, we show that at low temperature in monolayer MoS2, given quasi-localized excitons and consequently a significant inter-exciton spacing, the excitons undergo dipole-dipole interaction and annihilate one another in a manner analogous to Auger recombination. To design our model, we assume that each exciton is localized in a region whose length is on the same scale as the excitonic diameter, thus causing the exciton to behave in a fermion-like manner, while the distance between neighboring excitons is much larger than the exciton diameter. We construct the orbital ladder operators for each exciton and apply Fermi's Golden Rule to derive the overall recombination rate as a function of exciton density.

Microscopic Theory of Exciton-Exciton Annihilation in Two-Dimensional Semiconductors

“…[16] The wide spectrum of experimental results and the sensitivity of EEA to extrinsic effects call for a theoretical prediction of intrinsic EEA coefficients to quantify its effect on device performance. So far, there have been theory studies based on Fermi's golden rule with a k • p-model [17], Monte Carlo simulations of diffusion-assisted EEA [11] and a dipole-dipole interaction model assuming spatially localized excitons [18]. While these are low-energy models, it has been pointed out in Ref.…”