PHONONS IN SEMICONDUCTOR SUPERLATTICES

We present theoretical studies of phonon modes in semiconductor superlattices in a rigid-ion model. We examine the dispersion curves for phonons propagating in any directions, taking into account the long-range Coulomb interaction. We introduce an alternative approach which avoids direct computation of the Coulomb interaction in superlattices. Our calculations indicate that several superlattice optical phonon branches can have different frequencies when → k approaches zero from different directions. Such anisotropic splitting was observed experimentally and was interpreted in a macroscopic model involving layers of different dielectric constants. The predictions of our microscopic model are in qualitative agreement with those of the macroscopic model. © 1991.