Ultrafast carrier-carrier scattering among photoexcited nonequilibrium carriers in GaAs.

Abstract

We have studied carrier-carrier scattering in photoexcited electron-hole plasmas in GaAs at plasma densities from ${10}^{15}$ to ${10}^{17}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$, using numerical solution of the dynamically screened Boltzmann equation and classical molecular dynamics. The solution of the dynamically screened Boltzmann equation indicates that for excited electrons, scattering among the injected carriers is as important a scattering process as LO-phonon emission at densities greater than about 8\ifmmode\times\else\texttimes\fi{}${10}^{15}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$, and at ${10}^{17}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ the photoexcited electrons are nearly thermalized in 150 fsec. As a result of weaker screening, the interaction between carriers has a stronger effect in this case than when a low density of energetic electrons is immersed in a cool background plasma, where previous work has shown that carrier-carrier scattering becomes as significant as LO-phonon emission at a density of about 8\ifmmode\times\else\texttimes\fi{}${10}^{16}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. We also find that classical molecular-dynamics calculations are dominated by nonphysical effects at short times, arising from the pointlike nature of the simulated carriers.