Far Infrared Reflectance Spectroscopy Of AlAs-GaAs Microstructures

We report infrared reflectance spectra in the range 100-450 cm-1 for an AlAs-GaAs heterostructure and three AlAs-GaAs superlattices with different periods. All the spectra clearly exhibit the TO phonon modes of pure GaAs and AlAs and a sharp interference peak at the GaAs LO frequency. The heterostructure data yield a set of phonon parameters for unoxidised AlAs. The superlattice spectra exhibit additional structure between 225 and 400 cm-1 and a broadening of the GaAs TO peak. The long wavelength superlattice optical theory of Agranovich and Kravtsov explains most of the features of the superlattice reflectivity.