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

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/AlₓGa_1-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 that reveals anticrossing behavior. 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.