Interface Phonon Polariton Modes Research Articles

Electric-dipole absorption resonating with longitudinal optical phonon-plasmon system and its effect on dispersion relations of interface phonon polariton modes in metal/semiconductor-stripe structures

Interface phonon polaritons (IPhPs) in nano-structures excluding metal components are thoroughly investigated because they have lower loss in optical emission or absorption and higher quality factors than surface plasmon polaritons. In previous reports, it is found that strong infrared (IR) absorption is based on the interaction of p-polarized light and materials, and the resonance photon energy highly depends on the structure size and angle of incidence. We report the optical absorption by metal/semiconductor (bulk-GaAs and thin film-AlN)-stripe structures in THz to mid-IR region for the electric field of light perpendicular to the stripes, where both of s- and p-polarized light are absorbed. The absorption resonates with longitudinal optical (LO) phonon or LO phonon-plasmon coupling (LOPC) modes, and thus is independent of the angle of incidence or structure size. This absorption is attributed to the electric dipoles by the optically induced polarization charges at the metal/semiconductor, heterointerfaces, or interfaces of high electron density layers and depression ones. The electric permittivity is modified by the formation of these dipoles. It is found to be indispensable to utilize our form of altered permittivity to explain the experimental dispersion relations of metal/semiconductor-IPhP and SPhP in these samples. This analysis reveals that the IPhPs in the stripe structures of metal/AlN-film on a SiC substrate are highly confined in the AlN film, while the permittivity of the structures of metal/bulk-GaAs is partially affected by the electric-dipoles. The quality factors of the electric-dipole absorption are found to be 42–54 for undoped samples, and the value of 62 is obtained for Al/AlN-IPhP. It is thought that metal-contained structures are not obstacles to mode energy selectivity in phonon energy region of semiconductors.

Surface and interface phonon-polaritons in freestanding quantum well wire systems of polar ternary mixed crystals

The surface and interface phonon-polaritons in freestanding rectangular quantum well wire systems consisting of polar ternary mixed crystals are investigated in the modified random-element-isodisplacement model and the Born–Huang approximation, based on the Maxwell's equations with the boundary conditions. The numerical results of the surface and interface phonon-polariton frequencies as functions of the wave-vector, geometric structure, and the composition of the ternary mixed crystals in GaAs/AlxGa1−xAs and ZnxCd1−xSe/ZnSe quantum well wire systems are obtained and discussed. It is shown that there are 10 and 8 branches of surface and interface phonon-polaritons in the two quantum well wire systems respectively. The effects of the “two-mode” and “one-mode” behaviors of the ternary mixed crystals on the surface and interface phonon-polariton modes are shown in the dispersion curves.

Interface phonon-polaritons in quantum well wire systems of polar ternary mixed crystals

The interface phonon–polaritons in quasi-one-dimensional rectangular quantum well wire systems consisting of polar ternary mixed crystals have been investigated with the modified random-element-isodisplacement model and the Born–Huang approximation, combined the Maxwell’s equations and the boundary condition of electromagnetic field. The numerical results of the frequencies of interface phonon–polaritons as functions of the wave-vector, geometric structures, as well as composition x for the quantum well wire systems GaAs/AlxGa1−xAs and ZnxCd1−xSe/ZnSe are gained and discussed. It is shown that there are six branches of interface phonon–polariton modes in quantum well wire systems. The effects of “one mode” and “two mode” behaviors of the ternary mixed crystals on the interface modes are also shown in the dispersion curves.

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

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.

Surface phonon polariton characteristics of wurtzite ZnO thin film grown on silicon substrate

AbstractIn this work, p‐polarized far infrared attenuated total reflection (ATR) with Otto configuration technique is employed to study the surface phonon polariton (SPP) characteristics of wurtzite ZnO thin film grown on Si(111) substrate. One prominent dip corresponding to the leaky SPP mode of the ZnO is detected at 532 cm−1. The obtained result is in good agreement with the calculated ATR spectrum simulated based on the transfer matrix formulation. The origin of the observed dip is verified with the surface polariton dispersion curves based on a three anisotropic layer model (air–ZnO–Si). The results also reveal that the real SPP and the interface phonon polariton modes for this studied structure are barely observable experimentally.

Dispersion of Surface and Interface Phonon Polariton Modes in Wurtzite Based Multilayer System

Dispersion of the surface and interface phonon polariton modes in wurtzite based multilayer system is investigated theoretically. In this study, we present a new formulation of the surface polariton (SP) dispersion relation for wurtzite based multilayer system. The expression is derived through solving Maxwell's electromagnetic equations directly by using algebraic manipulation method. The formulation is general and can be applied on any wurtzite layered structures in which the total number of layers in the system is equal or greater than two. In practice, the theory is employed to simulate the SP dispersion curves for several wurtzite layered structures, i.e., vacuum/ZnO, vacuum/ZnO/6H-SiC and vacuum/ZnO/GaN/6H-SiC. The features of these SP dispersion curves are analyzed and discussed in detail. It is shown that the characteristics of layers and the thicknesses of layers in the system have an important influence on the dispersion properties of the surface and interface phonon polariton modes.

Surface and interface phonon polariton characteristics of wurtzite ZnO/GaN heterostructure

Surface and interface phonon polariton modes in wurtzite ZnO/GaN heterostructure on wurtzite 6H–SiC substrate were investigated by a variable angle p-polarized infrared attenuated total reflection spectroscopy. Three dips corresponding to the surface and interface phonon polariton modes were observed; two of the dips that having a lower intensity level of reflectivity were the leaky modes whereas, another one was a real mode. The observations were verified with the surface polariton dispersion curve simulated based on an anisotropy model for a four-layer system. It was shown that the frequencies of leaky modes are predictable by considering the damping of the substrate.

Studies of surface and interface phonon polariton characteristics of wurtzite ZnO thin film on wurtzite 6H-SiC substrate by p-polarized infrared attenuated total reflection spectroscopy

The surface and interface phonon polariton characteristics of a wurtzite ZnO thin film grown on a wurtzite 6H-SiC substrate are investigated by p-polarized infrared attenuated total reflection spectroscopy. Two absorption dips corresponding to the leaky surface phonon polariton (SPP) mode of ZnO and the interface phonon polariton (IPP) mode of ZnO/6H-SiC are clearly observed at 558 and 916cm−1, respectively. The observations are in good agreement with the results determined from the theoretical surface polariton dispersion curve simulated by means of an anisotropy model. Finally, the effects of the ZnO thin film thickness on the SPP and IPP modes are deduced from the theoretical calculations.

Interface phonon–polaritons in quantum well systems of polar ternary mixed crystals

The interface phonon–polaritons in quantum well systems consisting of polar ternary mixed crystals are investigated. The numerical results of the interface phonon-polariton frequencies in the GaAs/AlxGa1–xAs, ZnSxSe1–x/ZnS, and ZnxCd1–xSe/ZnSe quantum well systems are obtained and discussed. It is shown that there are six branches of interface phonon-polariton modes distributed in three bulk phonon-polariton forbidden bands in the systems. The electric fields of interface phonon–polaritons are also presented and show the interface locality of the modes. The effects of the ‘two-mode’ and ‘one-mode’ behaviours of the ternary mixed crystals on the interface phonon-polariton modes are shown in the dispersion curves.

P‐polarized infrared attenuated total reflection study of InN thin films grown on Si(111) substrate

AbstractWe report for the first time the surface phonon polariton (SPP) and interface phonon polariton (IPP) characteristics of InN thin films grown on AlN buffer layer on Si(111) substrate by molecular beam expitaxy. The p‐polarized infrared attenuated total reflection technique was used to excite the SPP and IPP modes of the sample. It was found that the SPP mode of InN and the IPP mode of InN/AlN were clearly ob‐ served at 609 cm–1 and 877 cm–1, respectively. The origins of the observed peaks were verified by theoretical simulations based on the anisotropic model. In general, a good agreement between the experimental and theoretical results was obtained. Finally, the effect of the free carriers on the SPP mode is discussed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Thickness Dependence of Surface and Interface Phonon-Polariton Modes in InN/AlN Nanolayers

We study the conditions for appearance and observation of surface and interface phonon-polariton (SPP and IPP) modes in thin InN layers grown on sapphire using AlN buffer. Theoretical dispersion relations of the IPP modes in the system air/InN/AlN/sapphire for different thickness of the InN layer are obtained. Features in the experimentally measured infrared reflectance were associated with the appearance of interface phonon-polariton excitations at wave-numbers between the TO and LO modes.

Surface and interface-related phonon modes in InN/AlN nanolayer structures

We study the conditions for appearance and observation of surface and interface phonon-polariton (SPP and IPP) modes in thin InN layers grown on sapphire using AlN buffer. Theoretical dispersion relations of the IPP modes in the system air/InN/AlN/sapphire for different thickness of the InN layer are obtained. Features, additional to those due to the compounds optical phonons, are observed. The asymmetry in the experimentally observed Raman mode peaks is associated with the appearance of interface phonon-polariton excitations at wave-numbers between the TO and LO modes, which are not reported by now.

Localized interface phonon polaritons in superlattice with a structural defect consisting of ternary mixed crystal

Abstract Using a transfer matrix method, we investigate the existence and characteristics of the localized interface phonon-polariton modes (IPPMs) in superlattice (SL) with a structural defect consisting of ternary mixed crystal (Al x Ga 1− x As). The results show that the introduction of two-mode behavior of the ternary mixed crystal leads to the rich and varied localized IPPMs spectra with new features. The characteristics and positions of the localized IPPMs in the Reststrahlen region are strongly dependent on the concentration x of the ternary mixed crystal. Moreover, it is found that the localized IPPMs are sensitive to the thicknesses of the defect and constituent layers as well as to the transverse wavenumber q ∥ .

Surface and interface phonon-polaritons in bilayer systems of polar ternary mixed crystals

The surface and interface phonon-polaritons in bilayer systems consisting of polar ternary mixed crystals are investigated in the modified random-element-isodisplacement model and the Born–Huang approximation, based on the Maxwell’s equations with the boundary conditions. The numerical results of the surface and interface phonon-polariton frequencies as functions of the wave vector and the composition of the ternary mixed crystals in GaAs/AlxGa1−xAs, ZnS/ZnSxSe1−x, and ZnSe/ZnxCd1−xSe bilayer systems are obtained and discussed. It is shown that there are six branches of surface and interface phonon-polaritons in binary/ternary systems. The effects of the “two-mode” and “one-mode” behaviors of the ternary mixed crystals on the surface and interface phonon-polariton modes are shown in the dispersion curves. The electric fields of surface and interface phonon-polaritons are also presented for various cases.

Localized interface phonon polaritons in two coupled semi-infinite superlattices

Using a transfer matrix method, we study the characteristics of the localized interface phonon polariton modes in two coupled superlattices (SLs) with a defect layer. Comparing different structure defects of SL where the dielectric characteristics of defect layers are different, we find that there are certain differences in the distribution and number of the localized interface phonon polariton modes in the Reststrahlen regions ［ωTO，ωLO］ and there are different characteristics for anti-symmetric modes in the above structures. The structuraly defective SL of which the dielectric constant of defect layer is independent of frequency was emphatically investigated. We found that the localized interface phonon polariton modes in such structure are sensitive to the thicknesses and order of the constituent layers, the thickness of the defect layer as well as the transverse wavenumber q∥.

The evolution of interface phonon–polariton modes in a finite superlattice with a structural defect

Using a transfer matrix method, we derive the dispersion equation for interface phonon–polariton modes (IPPMs) in a finite superlattice (SL) with a structural defect. The numerical results show that, in the nonradiative regime, there exist localized IPPMs (including retardation) inside or outside the Reststrahlen regions defined by the interval [ωTO, ωLO]. The localized IPPMs lie either in the minigaps or below and above the bulk bands, and their transversal electric field amplitudes are located in the vicinity of the defect layer or surface layers. The evolution of the IPPMs localized in the vicinity of a different interface can clearly be tracked. In addition, a brief analysis that radiative IPPMs evolve into nonradiative IPPMs is given.

Coupling of phonon-polariton modes at dielectric-dielectric interfaces by the ATR technique

We report the calculated ATR dispersion relation of the interface phonon-polariton modes in the prism-dielectric-dielectric configuration. Comparison of electromagnetic dispersion relations (EMDR) with the ATR dispersion relations are presented for three different interfaces: I) GaAs/GaP, II) CdF2/CaF2 and III) CaF2/GaP in two propagation windows, using the Otto and Kretschmann geometries for p-polarized light. We have studied the three cases using angle and frequency scans for each window and geometry. The results indicate that it is possible to excite and detect phonon-polariton modes at the dielectric-dielectric interface.