Nature of the electronic states in random dimer AlxGa1−xAs superlattices

We study the nature of the electronic states in one-dimensional disordered superlattices. We examine analytically and numerically the effects of short-range correlated disorder in Random Dimer Barrier Superlattices (RDBSL). The conductance and the localization length are statistically computed within an average procedure by means transfer matrix formalism to discriminate the nature of the electronic states in the miniband structure. We consider Al
_x
Ga
_1-x
As layers having identical thickness where the (Al) molar fraction x takes at random two different values with the constraint that one of them appears only in pairs, thus forming a RDBSL. We demonstrate that the superlattice supports two types of delocalized states; one of them comes from resonance effects at dimer barriers, while the other type is due to the commuting nature of the transfer matrices describing the system at certain energies. The states close to the resonance can be viewed as consisting of extended states. In the band tails, i.e. for vanishing conductance, the states are strongly localized.