INTERACTION BETWEEN AN ELECTRON AND OPTICAL PHONONS IN POLAR SEMICONDUCTOR HETEROSTRUCTURES

Interface phonons and bulk-like longitudinal-optical (LO) phonons and their interaction with an electron are studied for a finite four-layer heterostructure (FFLHS). An analysis of the field eigenvectors shows that, in the vicinity of the Brillouin-zone center, an interface trans verse-optical (TO) mode oscillates at the bulk LO frequency, and an in terface LO mode oscillates at the bulk TO frequency. Analytic expressi ons and numerical illustrations for dispersion relations of interface modes and for electron-phonon coupling functions and scattering rates are obtained for finite, semi-infinite and infinite quantum well (QW) structures which are important special cases of an FFLHS. It is shown that the scattering rates depend strongly on the well width of a QW st ructure, and that interface modes are much more important than bulk LO modes when the well width is small. The calculated results also show that the usual selection rules for intersubband and intrasubband trans itions break down in asymmetric heterostructures. Moreover, we have fo und an interesting result. That is, in comparison with the negligibly small interaction between an electron and the lowest-frequency interfa ce-mode in symmetric single QWs and commonly used step QWs, this inter action may be very large in asymmetric single QWs and general step QWs .