Picosecond Raman light-scattering study of hot carriers in InP

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Abstract
We demonstrate a novel method of using picosecond time-resolved Raman scattering to study the kinetics of nonequilibrium carriers in semiconductors. A pump–probe technique employing two separate lasers of different intensities, focal-spot sizes, and pulse durations is used to ensure that a plasma of uniform density is probed. The nonequilibrium-carrier density near the surface of a semi-insulating InP sample is estimated by fitting the photoexcited plasmon – longitudinal optic phonon coupled-mode peak in the Raman spectra. The dielectric function used in the calculation includes contributions from intraband transitions of electrons, light holes, and heavy holes as well as from interband transitions of the holes. The temporal evolution of the optically excited carrier population is modelled using a one-dimensional diffusion equation. The ambipolar diffusion constant and the surface-recombination velocity of the nonequilibrium carriers are found to be comparable to estimated values based on extrapolation of equilibrium properties.

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