Theory of excitonic complexes in gated WSe$_2$ quantum dots

TL;DR

This paper develops a comprehensive theory for excitonic complexes in gated WSe2 quantum dots, accounting for many-body interactions, spin, valley, and orbital effects, and predicts their optical properties under various conditions.

Contribution

It introduces an atomistic tight binding approach to model excitons in gated WSe2 quantum dots, incorporating detailed electronic structure and Coulomb interactions.

Findings

Electron-hole attraction depends on system parameters.

Confinement potential influences electron-hole pair stability.

Absorption spectrum can be predicted from computed states.

Abstract

Single-layer quantum dot gate potential causes type-II band alignment, i.e. electrostatically confines holes and repels electrons, or vice versa. Hence, the confinement of excitons in gated type II quantum dots involves a delicate balance of the repulsion of electrons due to the gate potential with the attraction caused by the Coulomb interaction with a hole localized in the quantum dot. This work presents a theory for neutral excitonic complexes within gated $\text{WSe}_\text{2}$ quantum dots, considering spin, valley, electronic orbitals, and many-body interactions. We analyze how the electron-hole attraction depends on a range of system parameters, such as screened Coulomb interaction, strength of confinement of holes, and repulsion of electrons. Using an atomistic tight binding model we compute valence and conduction band states within a computational box comprising over one million atoms with applied gate potential. The atomistic wavefunctions are then used to calculate direct and exchange Coulomb matrix elements for a fictitious type I quantum dot, and to obtain a spectrum of interacting electron-hole pairs. Next, we study the effect of repulsive potential, pulling away electrons from the valence hole. We determine whether electron-hole pairs are sufficiently attracted to overcome electron repulsion by the confinement potential. Finally, we compute the dipole transition between hole and electron states to obtain the absorption spectrum.