Folded acoustic and quantized optic phonons in (GaAl)As superlattices

Raman scattering studies of a variety of (GaAl)As superlattices grown by molecular-beam epitaxy are presented. Folded acoustic phonons appear as doublets in the Raman spectra. Their frequencies are accurately predicted by several models, including an approximate solution of an elastic continuum model through a perturbation approach. Scattering intensities of the folded acoustic modes are predicted by a photoelastic continuum model. Calculations on a layered dielectric continuum provide information about anisotropy of optical phonons. Linear-chain model calculations indicate that optical phonons in binary superlattices are largely confined to alternate layers. Peaks in the Raman data are identified with the resulting quantized optic modes. It is shown that Raman scattering has the potential to provide structural information similar to that which can be obtained by x-ray diffraction.