Interactions between extended and localized states in superlattices

We have observed electric-field-induced interactions between the extended states of a (40) -(15) GaAs-Ga0.65Al0.35As superlattice and the localized state of an 80- terminating GaAs well. At fields such that the energy of an extended state was close to that of the localized level, low-temperature (5-K) photocurrent spectra associated with interband transitions exhibited three pronounced doublets of peaks with characteristic resonant and anticrossing behavior. As the two levels approach each other, the initially asymmetrical peak intensities first become of comparable strengths and then exchange their roles in the resulting asymmetrical peak intensities as the states begin to repel each other. A comparison of the experimental results with numerical solutions of Schrödingers equation showed that the doublets result from the interaction of the localized state with the three superlattice states of highest energy, centered aroung its last three wells.