Coupled phonon-photon excitation field structure and dispersion in binary semiconductor superlattices are studied using a local theory with retardation. The material layers are characterized by the frequency-dependent isotropic dielectric permittivities. Numerical calculations have been carried out for GaAs/AlAs superlattices with the layer thickness ratio d 1/ d 2 < 1 and d 1/ d 2 > 1 in the case of in-plane propagation of p-polarized electromagnetic waves. Seven main dispersion branches and two series of additional ones related to confined modes are obtained. The latter are found to exist just below the transverse optical phonon frequencies of constituent materials. The branches characterized by different types of filed symmetry are found to intersect in the absence of damping. The conditions of the crossing points existance are estimated.