Spectral modulation of exciton Fano resonance due to Zener breakdown in strongly biased superlattices

The effects of the Wannier-Stark ladder (WSL) resonance on the optical absorption spectra of strongly biased superlattices are theoretically investigated. Exciton Fano resonance (FR) states in this system are calculated based on the multichannel scattering theory. When the bias of a static electric field (F) is applied such that a WSL subband state is energetically aligned with its adjacent ones, resulting in an anticrossing with strong repulsion due to Zener resonance, we obtain the following findings. (i) The onset of exciton absorption noticeably shifts toward the lower energy side, accompanying the oscillation of the magnitude of the absorption tail with the change in F . However, for the anticrossing, this effect is limited to a small localized region of F . In fact, a slight change in F away from the anticrossing leads to a peculiar suppression of the redshift of the absorption tail edge. (ii) The absorption intensities and the positions of the FR states vary in an irregular manner due to the Zener breakdown as F traverses the anticrossing region. For instances in a certain WSL state, the oscillator strength is reduced by a large extent only in the anticrossing region, followed by recovery of the intensity out of this region. Moreover, the changes in Fano’s q values with respect to F are also discussed. As described in (i) and (ii), these two effects on the exciton spectra are due to the delocalization of WSL wave functions across several periods that accompany the strong anticrossing