Propagation of Large-Wave-Vector Acoustic Phonons in Semiconductors

The spatial and temporal characteristics of phonon pulses generated in the interband energy relaxation process of photoexcited $e-h$ pairs in GaAs and InP are reported. With use of a superconducting Pb tunnel junction as a phonon threshold detector, it is shown that the energy transport occurs via near-zone-edge transverse acoustic phonons and that over lengths of the order of several millimeters the pulse propagation shows all features of ballistic transport in a dispersive medium.