COUPLING OF ELECTRONS TO INTERFACE PHONONS IN SEMICONDUCTOR QUANTUM-WELLS

In a recent paper [B. K. Ridley and M. Babiker, Phys. Rev. B 43, 9096 (1991)] the authors have argued that when retardation is taken into ac count the interface phonons of semiconductor superlattices obtained fr om the usual dielectric continuum approach are transverse polariton mo des and that they therefore do not couple to electrons via the strong Frohlich interaction. Here we show that the interface polaritons obtai ned from this dielectric continuum approach, in general, have both tra nsverse and longitudinal components and that the dispersion and charac ter of the modes are affected by retardation only for small wave vecto rs (k less than or similar omega(phonon)/c). For wave vectors of inter est in electron-phonon scattering, the interaction is given to a good approximation by the usual Frohlich interaction neglecting retardation .