Localized Energy States Induced by Atomic-Level Interfacial Broadening in Heterostructures

A theoretical framework incorporating atomic-level interfacial details is derived to include the electronic structure of buried interfaces and describe the behavior of charge carriers in heterostructures in the presence of finite interfacial broadening. Applying this model to ultrathin heteroepitaxial (SiGe)m/(Si)m superlattices predicts the existence of localized energy levels in the band structure induced by sub-nanometer broadening, which provides additional paths for hole-electron recombination. These predicted interfacial electronic transitions and the associated absorptive effects are confirmed experimentally at variable superlattice thickness and periodicity. By mapping the energy of the critical points, the optical transitions are identified between 2 and 2.5 eV thus extending the optical absorption to lower energies. This phenomenon enables a straightforward and non-destructive probe of the atomic-level broadening in heterostructures.