Observation of standing acoustic waves by resonant Raman scattering

Resonant Raman measurements on GaAs/GaP quantum wells, as thin as one monolayer, are reported. The work is focused on the low-frequency scattering range, which exhibits a continuous emission and periodic oscillations that have never been observed up to now. It is shown that spatial localization of electrons leads to Raman scattering processes for which momentum is not conserved, and hence to the activation of the density of states of acoustic phonons. A model, based on electron-acoustic phonon interaction, is developed and used for calculations of the resonant Raman efficiency. A good agreement with measured spectra is obtained. The origin of the observed periodic oscillations is interpreted by considering standing acoustic waves.