Influence of Fano Coupling on Wannier-Stark Transitions in Semiconductor Superlattices

Abstract

We report on the systematical investigation of Fano resonances in electrically biased semiconductor superlattices. In such quantum structures, Coulomb interaction couples discrete excitonic states of the Wannier-Stark ladder to continua of lower-lying subbands. In absorption these transitions show the typical asymmetric line shape of a Fano resonance. The unique feature of these Fano resonances is that they allow to continuously tune the key parameter — the coupling strength Γ between the discrete state and the degenerate continuum — by varying the bias voltage. Using this feature, we directly show that the Fano coupling leads to a fast polarization decay. We also investigate the dependence of the Fano parameters on the structure of the superlattice and compare to an extensive theoretical model of the resonances.