Superlattice with two δ-type defects: electronic structure and density of states

Abstract

The electronic-level structure and local density-of-states (LDOS) distributions are investigated for an infinite GaAs/AlxGa1−xAs superlattice (SL) with two strongly spatially confined defect layers (the so-called δ-defects). The energy spectrum is determined by using a multi-matching procedure within the envelope-function approximation, while the LDOS is computed via combined factorization and direct methods in the framework of the Green's function formalism. In general, insertion of two δ-defects leads to the appearance of two localized states inside the minigaps, whose energy positions and space-charge distributions can be tuned by adjusting the defect parameters. A substantial change in the LDOS distribution is also observed. In particular, the region consisting of n periods between the defected SL layers exhibits—for large enough δ-defect strengths—an energy spectrum of n quasi-discrete resonances within the miniband range, whereas outside this region the LDOS takes the form characteristic of semi-infinite SL's terminated at the defect sites.