Nature of the extended states in random dimer-barrier superlattices

We theoretically study electron transmission in intentionally disordered GaAs-Al _xGa _{1- x}As superlattices with structural short-range correlations in the Al mole fraction of the Al _xGa _{1- x}As layers. The Al mole fraction in the equal-width Al _xGa _{1- x}As layers takes at random two different values, but with the constraint that one of them only appears at random in pairs, while GaAs layers are identical. We demonstrate that the superlattice supports two types of extended states, one of them comes from resonance effects at dimer barriers, as it was already reported for random dimer well superlattices, while the other type arises as a consequence of the binary nature of this heterostructure. Conditions for their observation in transport experiments are discussed.