Fano resonances in semiconductor superlattices

We use semiconductor superlattices as a model system for the investigation of Fano resonances. In absorption the excitonic transitions of the Wannier- Stark ladder show the typical asymmetric line shape due to coupling to the continuum of lower-lying transitions. The unique feature of these Fano reso nances is that they allow to continuously tune the key parameter - the coup ling strength Gamma between the discrete state and the degenerate continuum - by varying the bias voltage. Using this feature, we directly show that t he Fano coupling leads to a fast polarization decay. We also investigate th e dependence of the Fano parameters on the structure of the superlattice an d compare with an extensive theoretical model of the resonances. (C) 2001 E lsevier Science B.V. All rights reserved.