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

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 ${\mathrm{MX}}_{2}$ (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. This technique enables accurate computation of both ground and excited excitonic states across a wide range of electric field strengths, overcoming limitations of previous perturbative approaches. 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 ${\mathrm{WX}}_{2}$ monolayers compared to ${\mathrm{MoX}}_{2}$ monolayers due to the smaller exciton reduced mass. Furthermore, the presence of a dielectric substrate and an increase in the number of ${\mathrm{MX}}_{2}$ layers enhance the exciton susceptibility to the electric field, lowering the critical field for dissociation. The dependence of exciton properties on the number of ${\mathrm{MX}}_{2}$ 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.