Theory of conductivity in superlattice minibands

Abstract

We have calculated the impurity-scattering–limited electrical conductivity for vertical transport in superlattice minibands. For sufficiently small carrier density and/or ‘‘large’’ disorder the collisional broadening Γ(μ) can be larger than the chemical potential μ. In such situations the quasiparticle approximation breaks down, and use of the conventional Bloch-Boltzmann transport theory is unreliable. Also, as the period of the superlattice increases, the ratio Γ(μ)/μ grows, resulting in a reduction of the mobility, leading eventually to Anderson localization. In addition, the carriers in the miniband become nondegenerate already at low temperatures, giving rise to a significant temperature dependence of the mobility. Furthermore, due to the unique shape of the Fermi surface of the superlattice the mobility becomes independent of the carrier density when the chemical potential exceeds the miniband width.