Polaritons in semiconductor multilayered materials.

Abstract

A distinctive feature of multilayered semiconductor structures lies in the fact that their reflectance and absorption spectra are strongly influenced by their stratified geometry. With use of a standard Green's-function technique, the concept of a local density of polariton modes is examined and its formulation in terms of planar impedances is carried out. This scattering-theoretic approach appears to be valid for materials with any graded dielectric response and allows detailed description of the spatial distribution of the electromagnetic energy in nonradiative or radiative polariton modes at a given frequency and wavelength. In a multilayered material, the influence of the interfacial structure of the sample on the spectral properties such as the reflectance and attenuated total reflection is depicted. Various semiconductor layered structures are considered and their spectral properties in both polarizations, transverse electric and transverse magnetic, are analyzed in terms of local density of polariton modes. This paper basically describes complex states built from interacting interfaces or confined states and accounts for their localization. In the transverse-magnetic polarization, the spatial distribution of modes demonstrates that multilayered structures are able to absorb electromagnetic energy by a process involving interfacial polaritons. Finally, the long-wavelength limit of our formalism will be developed further to explicitly show its connection with the well-known effective-medium theory and to discuss the importance of the form anisotropy of the superlattice structure.