Electric field-induced delocalization effects in GaAs/AlAs single- and double-period superlattices

We have studied the effect of an electric field absorption properties of superlattices containing two interacting minibands in two different types of structures. The first system is a superlattice with rather wide GaAs wells and ultrathin AlAs barriers. The second system is a double-period superlattice with alternating barrier thickness, giving rise to two coupled ("bonding" and "anti- bonding") minibands with a rather small energy minigap between them. In both cases, the first and second conduction minibands are sufficiently close in energy so that the associated Stark ladder states can be brought into resonance. These resonances, observed between states centered in adjacent and non-adjacent wells, manifest themselves by anticrossing effects which are a signature for delocalization. The experimental results are in reasonable quantitative agreement with numerical calculations.