Surface Density of Acoustic Phonons in GaAs

We calculate the surface density of acoustic phonons for GaAs(110) and relate it to the Brillouin elasto-optic cross section. A continuum of surfacelike excitations is found in good agreement with the position and the shape of the surface structure observed in the measured Brillouin spectrum. The role played by the optical absorption coefficient in determining different scattering mechanisms is also discussed.