Quasidiffusion and the localized phonon source in photoexcited Si

Abstract

Previous observations of heat pulses produced by localized photoexcitation of silicon do not support the predictions of phonon ``quasidiffusion'' via anharmonic decay and elastic scattering. Our experiments, with controlled boundary conditions, verify that quasidiffusive theory is relevant in Si under very weak photoexcitation. Beyond this domain a transition to a localized source of low frequency phonons is attributed to excited carrier interactions. Photoluminescence experiments confirm the presence of electron-hole droplets coincident with this localized phonon source.