Anisotropy and infrared response of the GaAs-AlAs superlattice

We report the first infrared phonon spectra (50-450 ${\mathrm{cm}}^{-1\mathrm{}}$) at oblique incidence (${\theta }_{\mathrm{inc}}={45}^{\circ }$) for the GaAs-AlAs superlattice. The spectra differ for $p$- and $s$-polarized radiation as calculated from long-wavelength superlattice optical response theory, showing that the superlattice resembles an anisotropic uniaxial crystal as predicted. The theory also gives phonon angular dispersion with implications for Raman scattering.