Exciton dissociation in two-dimensional transition metal dichalcogenides: Excited states and substrate effects

TL;DR

This study investigates how in-plane electric fields and substrates influence exciton dissociation in 2D transition metal dichalcogenides, revealing that substrates and layer number significantly affect the critical dissociation field.

Contribution

It provides a detailed theoretical analysis of exciton dissociation under electric fields in 2D TMDs, incorporating substrate effects and layer dependence, which was not comprehensively addressed before.

Findings

Electric field effectively dissociates excitons, especially excited states.

Substrate presence and increased layers lower the critical dissociation field.

Exciton properties depend on layer number, following power-law behavior.

Abstract

Exciton dissociation plays a crucial role in the performance of optoelectronic devices based on two-dimensional (2D) transition metal dichalcogenides (TMDs). In this work, we investigate the effect of an in-plane electric field on the exciton resonance states in MX$_2$ (M = Mo, W; X = S, Se) monolayers and few-layers using the complex coordinate rotation method and the Lagrange-Laguerre polynomial expansion of the wave function. The exciton properties are well described within the Mott-Wannier model incorporating the nonlocal Keldysh potential. Our calculations reveal that an electric field effectively dissociates excitons, with excited states being more easily dissociated than the ground state. The critical field for exciton dissociation is found to be smaller in WX$_2$ monolayers compared to MoX$_2$ monolayers due to the smaller exciton reduced mass. Furthermore, the presence of a dielectric substrate and an increase in the number of MX$_2$ layers enhance the exciton susceptibility to the electric field, lowering the critical field for dissociation. The dependence of exciton properties on the number of MX$_2$ layers can be well described by power functions. These findings provide valuable insights for the design and optimization of high-performance optoelectronic devices based on 2D TMDs.