Polar optical modes in semiconductor nanostructures

Polar optical modes play an important role in electron-phonon processes such as scattering rates, polaron effects and resonant Raman scattering in quantum wells and superlattices. Because of this there has been in recent years a strong interest in the development of a long-wave theory for optical modes in semiconductor nanostructures. This theory would be the equivalent of the effective mass theory for electrons. Besides microscopic calculations it should provide a satisfactory theoretical model to study the long-wave limit, to which most experimental evidence is circumscribed. Important elements in this type of theory are the inclusion of the bulk spatial dispersion of the optical modes together with the fact that, at an interface between two media, mechanical and electromagnetic boundary conditions must be satisfied. In some cases, like InAs/GaSb and related superlattices, the details of the interface structure are also important. We discuss here the different approaches employed to study the long-wave limit in these systems, including other approaches in which the envelope function model is derived directly from microscopic lattice dynamics.