From quantum dots to quantum dashes: Excitonic spectra of highly elongated InAs/InP nanostructures

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 a configuration interaction method for excitonic properties. Large nanostructure shape anisotropy leads to a peculiar trend of bright exciton splitting, which is quenched at a certain point with further shape elongation, contradicting predictions of simplified models. Moreover, strong shape elongation promotes pronounced optical activity of the dark exciton, which can reach a substantial 1% of the bright exciton intensity without application of any external fields. An atomistic calculation is augmented with an elementary phenomenological model expressed in terms of light-hole exciton admixture increasing with shape deformation. Also, excitonic complexes ${X}^{\ensuremath{-}}, {X}⁺$, and $XX$ are studied, and the correlations due to the presence of higher excited states are identified as key factors affecting excitonic binding energies and the fine structure.