Polariton Structure and Spectral Reflectance of Multilayered Semiconducting Materials

Sharply defined multilayered structure have been grown from a variety of semiconducting materials. In these thin-film structures the accumulation of interfaces gives rise to new excitation modes that can be found both in the phonon and plasmon energy ranges. The detailed polariton structure of a general stratified material, with either a finite or an infinite number of layers, can conveniently be assessed in terms of an exact continued-fraction expansion of its relevant response functions, which can be used to quantitatively account for reflectance measurements and attenuated total reflection (ATR). Calculations of the infrared polariton structure, reflectivity and ATR spectra of typical superlattices made of polar materials are presented. The formation of Bloch-like continua of modes and isolated surface or interface states are discussed.