POLAR OPTICAL MODES IN SEMICONDUCTOR NANOSTRUCTURES

Polar optical modes play an important role in electron-phonon processe s such as scattering rates, polaron effects and resonant Raman scatter ing in quantum wells and superlattices, Because of this there has been in recent years a strong interest in the development of a long-wave t heory for optical modes in semiconductor nanostructures. This theory w ould be the equivalent of the effective mass theory for electrons. Bes ides microscopic calculations it should provide a satisfactory theoret ical model to study the long-wave limit, to which most experimental ev idence is circumscribed. Important elements in this type of theory are the inclusion of the bulk spatial dispersion of the optical modes tog ether with the fact that, at an interface between two media, mechanica l and electromagnetic boundary conditions must be satisfied, In some c ases, like InAs/GaSb and related superlattices, the details of the int erface structure are also important. We discuss here the different app roaches employed to study the long-wave limit in these systems, includ ing other approaches in which the envelope function model is derived d irectly from microscopic lattice dynamics.