Coupled free-carrier and exciton relaxation in optically excited semiconductors

Abstract

The energy relaxation of coupled free-carrier and exciton populations in semiconductors after low-density ultrafast optical excitation is studied through a kinetic approach. The set of semiclassical Boltzmann equations, usually written for electron and hole populations only, is complemented by an additional equation for the exciton distribution. The equations are coupled by reaction terms describing phonon-mediated exciton binding and dissociation. All the other relevant scattering mechanisms, such as carrier-carrier, carrier-phonon, and exciton-phonon interactions, are also included. The resulting system of rate equations in reciprocal space is solved by an extended ensemble Monte Carlo method. As a first application, we show results for the dynamics of bulk GaAs in the range from 1 to ϳ200 ps after photoexcitation. The build-up of an exciton population and its sensitivity to the excitation conditions are discussed in detail. As a consequence of the pronounced energy dependence of the LO-phonon-assisted transition probabilities between free-pair states and excitons, it is found that the efficiency of the exciton-formation process and the temporal evolution of the resulting population are sensitive to the excitation energy. We discuss the effects on luminescence experiments.

An Analysis of Electron-Hole Recombination in Solid Xenon with Time-Resolved Luminescence Spectroscopy

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Hot Carrier Relaxation by Extreme Electron-LO Phonon Scattering in GaN

“…This could explain the persistence of phonon replicas in the simulations which were not observed experimentally. Clearly, the validity of the simulation is limited by the neglect of excitonic effects, not only in the optical response function used, but also in the scattering channel through which excitons are formed during carrier relaxation [7].…”

Influence of non-collisional laser heating on the electron dynamics in dielectric materials

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