Optical time-of-flight investigation of the exciton transport in silicon

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Abstract
The transport of carriers created at the surface of a silicon sample by a short laser pulse is investigated by a new optical time-of-flight technique. This method is based on the excitation of charge carriers in a small region of the sample and the subsequent time-resolved detection of the carrier density at a well-defined distance. This provides direct access to the carrier velocity and the carrier density distribution. In the low-temperature regime investigated here the carrier transport is shown to be performed by free excitons. A comparison of the experiment with a hydrodynamic model yields an exciton diffusivity of D=300T−1/2 cm2/s. It is shown that acoustic-phonon scattering via the deformation potential is the dominating scattering process.