Folded acoustic phonons in (Al,Ga)As quasiperiodic superlattices

We have investigated Raman scattering by acoustic phonons in (Al,Ga)As Fibonacci superlattices grown by molecular-beam epitaxy. Many sharp doublet peaks, which are analogous to those produced by Raman scattering by folded acoustic phonons in periodic superlattices, appear at nonequal intervals in the Raman spectra. Assuming that the quasiperiodicities originating in the Fibonacci sequence cause zone-folding effects on acoustic phonons, folded-phonon frequencies calculated using an elastic continuum model are in good agreement with observed doublet-peak frequencies. We also discuss the intensity profiles of Raman scattering by folded phonons on the basis of a photoelastic model.