Quasidiffusion and the localized phonon source in photoexcited Si

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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.