QUASIDIFFUSION AND THE LOCALIZED PHONON SOURCE IN PHOTOEXCITED SI

Previous observations of heat pulses produced by localized photoexcita tion of silicon do not support the predictions of phonon ''quasidiffus ion'' via anharmonic decay and elastic scattering. Our experiments, wi th controlled boundary conditions, verify that quasidiffusive theory i s relevant in Si under very weak photoexcitation. Beyond this domain a transition to a localized source of low frequency phonons is attribut ed to excited carrier interactions. Photoluminescence experiments conf irm the presence of electron-hole droplets coincident with this locali zed phonon source.