Incident-photon energy dependence of Raman-scattering profiles by folded acoustic phonons in GaAs/AlAs superlattices

We present experimental and theoretical studies of the intensity of the upper frequency mode relative to the lower one in the doublet Raman band of the first-folded longitudinal-acoustic phonon, I(+1)/I(-1), as a function of an incident-photon energy in (GaAs)ₘ(AlAs)ₘ superlattices with m=8, 10, and 12 monolayers. It is found experimentally that the value of I(+1)/I(-1) depends on the energy of an incident Ar⁺-laser line from 4765 to 5145 A{}. Here, on the basis of an effective-mass approximation for the electronic structures and an elastic continuum approximation for the phonon modes, we propose a simplified formula for the incident-photon energy dependence of I(+1)/I(-1), rather than considering all the quantum processes of electron-photon and electron-phonon interactions. The calculations indicate that the experimental results are mainly due to resonant effects of the electronic transitions between the second subbands of electrons and holes.