Dispersion Characteristics Of Guided Wave Phonon Polaritons In Slabs Of Ternary Mixed Crystals

Ternary mixed crystals have many excellent properties that binary crystals do not possess,and semiconductor films have extensive applications in solar cells,wireless communications,integrated circuits,light-emitting diodes,multifunctional protective coatings,semiconductor devices,liquid crystal displays,magneto-optical memories.At the same time,guided wave phonon polaritons also have a large number of applications in the field of integrated optics,therefore it is meaningful to study the wave guided phonon polaritons in ternary mixed crystal film systems.In this thesis the dispersion relations and the spatial distribution of the electric field of the guided wave phonon polaritons localized in the ternary mixed crystal slab and bilayer systems,as well as the variation of the energies of the guided wave modes with the composition of the ternary mixed crystal and the film thickness are investigated by using the modified random-element-isodisplacement model and the Born-Huang approximation,combined with Maxwell’s equations and the boundary conditions,and the experimental observability of the guided wave modes is also analyzed.The results obtained are as follows:1.The dispersion properties and related problems of guided wave phonon polaritons in slab systems of ternary mixed crystal are studied.The numerical results of the dispersion relation and the spatial distribution of electric field of guided wave phonon polaritons,and energies of the guided wave modes vary with the composition and film thickness of ternary mixed crystals for slabs of Al_xGa_1-xAs and Zn_xCd_1-xS.It is shown that there are three groups of guided wave phonon polariton modes in the ternary mixed crystal film system,each group of guided wave phonon polariton modes is composed of many discrete guided wave modes,and they are respectively located in the three frequency regions enclosed by the dispersion curves of photons in vacuum,the dispersion curves of bulk phonon polaritons,and the frequency curves of bulk longitudinal and transverse optical phonon of ternary mixed crystal.With the increase of ternary mixed crystal composition,the energies of two groups of guided wave modes increase nonlinearly,while those of the other group decrease nonlinearly.In addition,except for one mode whose frequency hardly changes with the film thickness,the frequencies of the other guided wave modes decrease nonlinearly with the increase of the film thickness.2.We have investigated the dispersion properties and related problems of guided wave phonon polaritons in bilayer systems consisting of ternary mixed crystal.The dispersion relation and the spatial distribution of electric field of guided wave phonon polaritons,and energies of the guided wave modes vary with the composition of ternary mixed crystals and film thickness for bilayer system Ga As/Al_xGa_1-xAs and Zn Se/Zn_xCd_1-xSe have been calculated.The results show that there are four and three groups of guided wave phonon polaritons in ternary mixed crystal bilayer system Ga As/Al_xGa_1-xAs and Zn Se/Zn_xCd_1-xS respectively.Each group of guided wave phonon polaritons is made up of many discrete guided wave modes,and they are distributed in different frequency regions enclosed by the dispersion curve of photons in vacuum,the dispersion curves of bulk phonon polaritons of binary crystals and ternary mixed crystals,and the long wave transverse and longitudinal optical phonon frequency curves of binary crystals and ternary mixed crystals.When the composition of ternary mixed crystal increases,for Ga As/Al_xGa_1-xAs bilayer system,the frequencies of three groups of guided wave modes decrease nonlinearly,while the frequencies of one other group of guided wave modes increase nonlinearly.For the bilayer system Zn Se/Zn_xCd_1-xSe,the frequencies of two groups of guided wave modes decrease nonlinearly,while the frequencies of one other group of guided wave modes increase nonlinearly.In addition,the energies of most guided wave modes also exhibit nonlinear change with the increase of film thickness of binary crystal and ternary mixed crystal respectively.