ULTRAFAST ACOUSTIC-PHONON BALLISTICS IN SEMICONDUCTOR HETEROSTRUCTURES

Using a two-color ultrafast surface deflection spectroscopy, we demons trate the time-resolved observation of acoustic phonon wave packets em itted from a single buried GaAs quantum well. A longitudinal acoustic phonon pulse is generated at a preselected depth within a highly confi ned 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 tile surface resolves propagating high-wave-vector ballistic phono ns sind quasiballistic or ''snake'' phonons which subsequently merge i nto a quasidiffusive phonon pulse.