Surface Polaritons Due to the Folded Optical Phonons in GaAs/AlAs Superlattices

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We have measured attenuated-total-reflection (ATR) spectra of GaAs/AlAs superlattice (SL) in the infrared region from 250 cm⁻¹ to 600 cm⁻¹. Around frequencies of GaAs (269 cm⁻¹) and AlAs (362 cm⁻¹) TO phonons, we have found a reduction of reflectance produced by the excitation of surface phonon polaritons, being associated with the fine structures in ATR spectra which stem from the folded optical phonons in the SL. We have moreover evaluated the dielectric parameters of GaAs and AlAs through theoretical ATR spectra fit to experimental ones. It has been found that the collision frequencies of TO phonon in the GaAs and AlAs layers employed here are much smaller than those obtained previously by other researchers.