Interfaces are ubiquitous in semiconductor low-dimensional systems used in electronics, photonics, and quantum computing. Understanding their atomic-level properties has thus been crucial to controlling the basic behavior of heterostructures and optimizing the device performance. Herein, we demonstrate that subnanometer interfacial broadening in heterostructures induces localized energy states. This phenomenon is predicted within a theory incorporating atomic-level interfacial details obtained by atom probe tomography. The experimental validation is achieved using heteroepitaxial (Si1-xGex)m/(Si)m superlattices as a model system demonstrating the existence of additional paths for hole-electron recombination. These predicted interfacial electronic transitions and the associated absorptive effects are evaluated 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 is shown to provide an optical fingerprint for a straightforward and nondestructive probe of the subnanometer broadening in heterostructures.
Keywords: Si/SiGe heterostructures; atomic disorder; epitaxy; interfacial broadening; localized state; optical absorption.