From Quantum Dots to Quantum Dashes: Excitonic Spectra of Highly Elongated InAs/InP Nanostructures

TL;DR

This study investigates how extreme elongation of InAs/InP nanostructures affects excitonic spectra, revealing unexpected behaviors like exciton splitting quenching and dark exciton optical activity, using atomistic theoretical modeling.

Contribution

It introduces a detailed atomistic approach combining tight binding and configuration interaction to analyze excitonic properties in elongated nanostructures, highlighting effects of shape anisotropy.

Findings

Bright exciton splitting is quenched at high elongation.

Dark exciton gains significant optical activity without external fields.

Higher excitonic complexes show correlation effects influencing binding energies.

Abstract

A transition from a cylindrical quantum dot to a highly elongated quantum dash is theoretically studied here with an atomistic approach combining empirical tight binding for single particle states and configuration interaction method for excitonic properties. Large nanostructure shape anisotropy leads to a peculiar trend of the bright exciton splitting, which at certain point is quenched with further shape elongation, contradicting predictions of simplified models. Moreover strong shape elongation promotes pronounced optical activity of the dark exciton, that can reach substantial $1\%$ fraction of the bright exciton intensity without application of any external fields. An atomistic calculation is augmented with a elementary phenomenological model expressed in terms of light-hole exciton add-mixture increasing with the shape deformation. Finally, exctionic complexes $X^-$, $X^+$, and $XX$ are studied as well and the correlations due to presence of higher excited states are identified as a key-factor affecting excitonic binding energies and the fine structure.