Doublet structures in quantum well absorption spectra due to Fano-related interference

TL;DR

This theoretical study predicts a novel Fano-related interference effect in quantum well absorption spectra, revealing doublet structures and anticrossing behavior due to strong valence-band mixing, challenging previous simple models.

Contribution

It introduces a new understanding of Fano-like interference involving a discrete state outside the continuum in quantum wells, with detailed predictions of spectral features.

Findings

Doublet structures form as the discrete state approaches the continuum.

The minimum separation energy depends on well width and is larger for narrow wells.

Previous simple models are insufficient to explain these phenomena.

Abstract

In this theoretical investigation we predict an unusual interaction between a discrete state and a continuum of states, which is closely related to the case of Fano-interference. It occurs in a GaAs/AlxGa1-xAs quantum well between the lowest light-hole exciton and the continuum of the second heavy-hole exciton. Unlike the typical case for Fano-resonance, the discrete state here is outside the continuum; we use uniaxial stress to tune its position with respect to the onset of the continuum. State-of-the art calculations of absorption spectra show that as the discrete state approaches the continuum, a doublet structure forms which reveals anticrossing behaviour. The minimum separation energy of the anticrossing depends characteristically on the well width and is unusually large for narrow wells. This offers striking evidence for the strong underlying valence-band mixing. Moreover, it proves that previous explanations of similar doublets in experimental data, employing simple two-state models, are incomplete.