High-frequency conductivity of superlattices with electron-phonon coupling

The high-frequency and long-wavelength conductivity due to electron--optical-phonon interaction was derived for superlattices made out of polar or partially polar semiconductors. The treatment for conductivity rests on Kubo's formula for the conductivity and the temperature-dependent Green's-function formalism. General expressions for the conductivity and the resistivity have been derived, and we have performed numerical calculations for a simple model in which the subband structures of the phonons are ignored and the electronic wave function is approximated by a periodic array of two-dimensional electron gases.