Surface and interface phonon-polaritons in four layer systems consisting of polar ternary mixed crystals

Abstract

Surface and interface phonon-polaritons in a four-layer (vacuum/polar binary crystal slab/polar ternary mixed crystal slab/polar binary crystal substrate) system are investigated with the modified random-element-isodisplacement model and the Born-Huang approximation, based on the Maxwell's equations with the usual boundary conditions. The numerical results of the surface and interface phonon-polariton frequencies as functions of the wave-vector, composition x, and thickness of slab in the two four-layer systems, i.e., AlxGa1-xAs/GaAs and ZnxCd1-xSe/ZnSe, are obtained and discussed. It is shown that there are seven branches of surface and interface phonon-polariton modes in the heterostructure systems, and that the frequencies of the surface and interface modes vary non-linearly with the composition and thickness of slab. The “one mode” and “two mode” behaviors of the ternary mixed crystals are also shown in the dispersion curves.