Acoustic-phonon Raman scattering in InAs/InP self-assembled quantum dots

Single layers of self-assembled InAs/InP quantum dots (QD) are studied by Raman scattering excited in resonance with the confined $E_1$ transition of InAs. Intense periodic oscillations are observed in the low-frequency Stokes and anti-Stokes spectra of both capped and uncapped QD. By using a controlled chemical etching, we progressively reduced the thickness of the InP cap layer. We found that the oscillations period is determined by the sample surface-QD layer separation and by the sound velocity of the longitudinal acoustic phonons. A model based on the interaction between confined electronic states and standing sound waves due to the sample surface showed a reasonable agreement with the measurements. The dependence of the low-frequency scattering on QD size is discussed.