Stark localization of a pair of coupled minibands in a GaAs/AlAs double-period superlattice

The electric-field dependence of the Stark-ladder structure of a strongly coupled GaAs/AlAs double-period superlattice with alternating AlAs barrier widths is investigated. At zero field, there are two conduction minibands with a small energy minigap between them. These minibands are caused by the bonding and antibonding states of the individual double periods due to the coupling induced by the ultrathin barriers. With increasing electric field, these minibands split into two coupled Stark ladders, showing a hierarchy of anticrossing effects. At very large fields, Stark localization within one-half of the double period gives rise to one single Stark ladder which is only slightly perturbed by the alternating barrier width. We present numerical calculations that show reasonable qualitative and quantitative agreement with the observed field effects.