Optical-phonon modes in superlattices

Publisher Website
Google Scholar
Abstract
We have studied optical-phonon modes associated with a finite wave vector parallel to the interfaces in a model superlattice in which the long-range Coulomb interactions are dealt with rigorously. Owing to the Coulomb interaction and the superlattice periodicity, for nonvanishing wave vector parallel to the interfaces, the modes are a hybrid of the longitudinal- and transverse-optical waves from the corresponding bulk materials. Compared to the bulklike mode with a weaker hybridization of the LO and TO waves, the so-called Coulomb mode (roughly corresponding to the interface mode in the dielectronic continuum model) exhibits stronger hybridization because of its dominant long-wavelength component. This distinguishes the Coulomb mode from the bulklike mode. The mode frequencies derived from the dielectric continuum model and the present microscopic model are essentially similar, provided the bulk phonons are dispersionless, but the vibrational wave functions calculated with the two models are different. When the dispersion of the bulk phonons is taken into account, the Coulomb modes obtained from the microscopic model lose the characteristics predicted by the dielectric continuum model.