Ultrafast acoustic phonon ballistics in semiconductor heterostructures

Using a two-color ultrafast surface deflection spectroscopy, we demonstrate the time-resolved observation of acoustic phonon wave packets emitted from a single buried GaAs quantum well. A longitudinal acoustic phonon pulse is generated at a preselected depth within a highly confined region (greater than or equal to 10 nm thick) through the coherent nonequilibrium deformation potential which was previously unobserved in such structures. Subsequent detection with subpicosecond resolution at the surface resolves propagating high-wave-vector ballistic phonons sind quasiballistic or "snake" phonons which subsequently merge into a quasidiffusive phonon pulse.