Three-Particle Complexes in Two-Dimensional Semiconductors

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).