Theoretical investigation of electron-hole complexes in anisotropic two-dimensional materials

TL;DR

This paper provides a theoretical analysis of electron-hole complexes like trions and biexcitons in anisotropic 2D materials, revealing high binding energies and anisotropic structures in phosphorene and arsenene.

Contribution

It introduces a detailed effective mass theory for these complexes in anisotropic 2D materials, with explicit results for phosphorene and arsenene.

Findings

Trions have high binding energies and elongated structures along the armchair direction.

Biexciton binding energies are significantly larger in phosphorene than in transition metal dichalcogenides.

Electron-hole complexes show strong anisotropic characteristics influenced by effective mass differences.

Abstract

Trions and biexcitons in anisotropic two-dimensional materials are investigated within an effective mass theory. Explicit results are obtained for phosphorene and arsenene, materials that share features such as a direct quasi-particle gap and anisotropic conduction and valence bands. Trions are predicted to have remarkably high binding energies and an elongated electron-hole structure with a preference for alignment along the armchair direction, where the effective masses are lower. We find that biexciton binding energies are also notably large, especially for monolayer phosphorene, where they are found to be twice as large as those for typical monolayer transition metal dichalcogenides.