Abstract
Excitonic effects play a particularly important role in the optoelectronic behavior of two-dimensional semiconductors. To facilitate the interpretation of experimental photoabsorption and photoluminescence spectra we provide (i) statistically exact diffusion quantum Monte Carlo binding-energy data for a Mott-Wannier model of (donor/acceptor-bound) excitons, trions, and biexcitons in two-dimensional semiconductors in which charges interact via the Keldysh potential, (ii) contact pair-distribution functions to allow a perturbative description of contact interactions between charge carriers, and (iii) an analysis and classification of the different types of bright trion and biexciton that can be seen in single-layer molybdenum and tungsten dichalcogenides. We investigate the stability of biexcitons in which two charge carriers are indistinguishable, finding that they are only bound when the indistinguishable particles are several times heavier than the distinguishable ones. Donor/acceptor-bound biexcitons have similar binding energies to the experimentally measured biexciton binding energies. We predict the relative positions of all stable free and bound excitonic complexes of distinguishable charge carriers in the photoluminescence spectra of WSe$_2$ and MoSe$_2$.
Highlights
The last decade has witnessed a remarkable surge of interest in the properties of truly two-dimensional (2D), atomically thin semiconductors
The nonhydrogenic nature of the excitonic energy spectrum is due to lateral polarization effects in 2D crystals, which modify the form of the Coulomb interaction between charge carriers
Our total-energy and pair distribution function (PDF) calculations were carried out using the variational quantum Monte Carlo (VMC) and diffusion quantum Monte Carlo (DMC) approaches [34,35]
Summary
The last decade has witnessed a remarkable surge of interest in the properties of truly two-dimensional (2D), atomically thin semiconductors. These include monolayer transition-metal dichalcogenides (TMDCs) such as MoS2, MoSe2, WS2, and WSe2, which acquire a direct-gap character in hexagonal. A interesting aspect of monolayer TMDCs is the strong excitonic effects present in their photoabsorption and photoluminescence spectra [5,6,7], including nonhydrogenic Rydberg spectra [8,9] and lines ascribed to trions (charged excitons) [10,11,12] and biexcitons (bound pairs of excitons) [13,14,15,16]. Mott-Wannier models of 2D trions and biexcitons have been studied using quantum Monte Carlo (QMC) methods [17,18,19,20,21,22,23,24,25], variational methods [26,27,28], and
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