Dynamical Excitonic Effects in Doped Two-Dimensional Semiconductors

Abstract

It is well-known that excitonic effects can dominate the optical properties of two-dimensional materials. These effects, however, can be substantially modified by doping free carriers. We investigate these doping effects by solving the first-principles Bethe-Salpeter equation. Dynamical screening effects, included via the sum-rule preserving generalized plasmon-pole model, are found to be important in the doped system. Using monolayer MoS2 as an example, we find that upon moderate doping, the exciton binding energy can be tuned by a few hundred millielectronvolts, while the exciton peak position stays nearly constant due to a cancellation with the quasiparticle band gap renormalization. At higher doping densities, the exciton peak position increases linearly in energy and gradually merges into a Fermi-edge singularity. Our results are crucial for the quantitative interpretation of optical properties of two-dimensional materials and the further development of ab initio theories of studying charged excitations such as trions.

Excitonic effects in the optical properties of 2D materials:an equation of motion approach

“…As noted before a finite Fermi energy comes from the spontaneous negative doping observed in TMDC's samples. The better agreement with the data shown in figure (14) relatively to the results of figure (13) shows the non-negligible effect of the doping in the optical properties. On the other hand, the parameter r 0 should also be a function of the electronic density.…”

“…This seems be the reason [14] why the B-series is not visible in WX 2 when the material is electron-doped (see figure 14). To conclude, given the uncertainties in the experimental data reported in table 3 we consider the agreement between our calculation and the data to be quite good.…”

“…This has attracted a wealth of scientific research [7,8,9,10,11,12,13,14,15,16,17,18,19,20,22,23]. The signature of excitons appeared first in the optical measurements of monolayer MoS 2 [5], where two peaks in the absorbance, with energies ∼ 1.9 eV and ∼ 2.1 eV, were identified.…”

Optically Discriminating Carrier-Induced Quasiparticle Band Gap and Exciton Energy Renormalization in MonolayerMoS2

“…The approximate reduction of defect PL yield at 2.64 eV is 2%. Using the linear trend fitted markedly differently in response to changes in carrier density [28,45]. For example,…”

“…Importantly, renormalization effects on the quasiparticle band gap and exciton binding energy tend to counteract each other, leading to only minimal changes in the optical band gap [28]. Thus, in conventional optical absorption spectroscopy, without direct identification of the quasiparticle band gap, quasiparticle and excitonic renormalization effects must be inferred from higherlying excitonic states [25,27,29,30].…”