Surface phonon polaritons in a semi-infinite superlattice with a cap layer consisting of ternary crystal

We study the existence and characteristics of the surface phonon polariton modes (SPPMs) in a semi-infinite superlattice (SL) with a cap layer consisting of ternary crystal AlxGa1−xAs. Our numerical results show that the introduction of the ternary mixed crystal leads to new SPPMs and varies the SPPMs spectra. The SPPMs may be situated in minigaps or below and above bulk bands, their positions in Reststrahlen region are strongly dependent on the concentration x   of the ternary crystal. Moreover, it is found that the SPPMs are sensitive to the thicknesses of the cap and constituent layers as well as the transverse wavenumber q∥q∥.