Three-Particle Complexes in Two-Dimensional Semiconductors

Abstract

We evaluate binding energies of trions X±, excitons bound by a donor or acceptor charge X^{D(A)}, and overcharged acceptors or donors in two-dimensional atomic crystals by mapping the three-body problem in two dimensions onto one particle in a three-dimensional potential treatable by a purposely developed boundary-matching-matrix method. We find that in monolayers of transition metal dichalcogenides the dissociation energy of X^{±} is typically much larger than that of localized exciton complexes, so that trions are more resilient to heating, despite the fact that their recombination line in optics is less redshifted from the exciton line than the line of X^{D(A)}.

Binding energies and spatial structures of small carrier complexes in monolayer transition-metal dichalcogenides via diffusion Monte Carlo

“…However, since binding energies for trions and biexcitons are extracted with reference to the exciton binding energy, the use of variational wave functions for all excitonic complexes leads to binding energies that need not provide a lower bound to the "exact" value, and it is unclear how much error cancellation occurs as a result. For the trion binding energy, Ganchev et al have discovered a remarkable exact solution, but only for the case where the full Keldysh effective potential is replaced with a completely logarithmic form that is accurate only at short range [39]. It is the purpose of this work to investigate the nature and accuracy of these approximate solutions by comparing with numerically exact results, and thereby to provide insights into the properties of higher-order excitonic complexes in two-dimensional TMDCs.…”

“…In addition, DMC allows a full sampling of the square of the wavefunction, which can be used to extract insight into the structure of small bound carrier assemblies. Although DMC has previously been used to calculate ground-state properties for trions interacting with a purely logarithmic potential [39], to the best of our knowledge it has not been used to calculate trion properties with the more realistic electron-hole interaction above, nor has it been used to calculate the properties of biexcitons. It should be noted that while the present work was underway, a numerically exact finite temperature path integral Monte Carlo (PIMC) study of excitons, trions, and biexcitons using the full Keldysh effective potential appeared [50].…”

“…These two potentials represent the asymptotic small and large r behavior, respectively, of (2). The purely logarithmic potential approximation has been employed by Ganchev et al in their analytical treatment of trions in TMDCs [39] while the Coulomb potential is the standard form for three-dimensional semiconductors. We find that a purely logarithmic potential overbinds the trion and results in binding energies about 50% larger than those reported by experiments.…”

Large Excitonic Reflectivity of MonolayerMoSe2Encapsulated in Hexagonal Boron Nitride

“…Excitonic transitions in TMD monolayers exhibit large oscillator strengths (14-16), resulting in large radiative linewidths compared to excitons in other semiconductor systems. In addition, the excitonic response in monolayers can be controlled electrically via gate-induced doping and by shifting the chemical potential (17)(18)(19).Importantly, these monolayers can be easily integrated with other 2D materials via Van der Waals stacking to improve their quality or add new functionalities. One of the most studied amongst such heterostructures is a TMD monolayer encapsulated by two hexagonal boron nitride 4 (hBN) flakes: this "passivated" monolayer exhibits enhanced carrier mobility (19,20) and reduced photoluminescence linewidth (21,22).…”

“…Excitonic transitions in TMD monolayers exhibit large oscillator strengths (14)(15)(16), resulting in large radiative linewidths compared to excitons in other semiconductor systems. In addition, the excitonic response in monolayers can be controlled electrically via gate-induced doping and by shifting the chemical potential (17)(18)(19).…”