Atomistic theory of dark excitons in self-assembled quantum dots of reduced symmetry

TL;DR

This study uses an atomistic model to analyze how shape symmetry breaking in self-assembled InAs/GaAs quantum dots influences the energy levels and optical activity of dark excitons, aligning with experimental observations.

Contribution

It introduces a detailed atomistic approach to understand the impact of symmetry reduction on dark exciton properties in quantum dots.

Findings

Symmetry reduction alters dark exciton polarization from axial to cross-linear.

Dark exciton dipole moments become polarized perpendicular to the growth axis.

Model results quantitatively match recent experimental data.

Abstract

We use an atomistic model to consider the effect of shape symmetry breaking on the optical properties of self-assembled InAs/GaAs quantum dots. In particular, we investigate the energy level structure and optical activity of the lowest energy excitons in these nanostructures. We compare between quantum dots with two-fold rotational and two reflections (C2v) symmetry and quantum dots in which this symmetry was reduced to one reflection only (Cs) by introducing a facet between the quantum dots and the host material. We show that the symmetry reduction mostly affects the optical activity of the dark exciton. While in symmetric quantum dots, one of the dark exciton eigenstates has a small dipole moment polarized along the symmetry axis (growth direction) of the quantum dot, in non-symmetric ones, the two dark excitons' dipole moments are predominantly cross-linearly polarized perpendicular to the growth direction and reveal pronounced polarization anisotropy. Our model calculations agree quantitatively with recently obtained experimental data.