Nature of the eigenstates in the miniband of random dimer-barrier superlattices

The dc conductance, the universal quantum fluctuations and the resistance distribution are numerically investigated in dimer semiconductor superlattices by means of the transfer matrix formalism. We are interested in the GaAs/Al_x Ga _1 − xAs layers, having identical thickness, where the aluminium concentration x takes, at random, two different values, with the constraint that one of them appears only in pairs, i.e. the random dimer barrier (RDB). These systems exhibit a miniband of extended states, around a critical energy, lying to the typical structure of the dimer cell. The states close to this resonant energy consist of weakly localized states, while in band tails i.e. for negligible conductance, the states are strongly localized. This is evidence of the suppression of localization in the RDB superlattices. The nature of the transition between these two regimes is quantitatively investigated through relevant physical quantities. The model is, hence, clearly and statistically examined.