Importance of carrier-carrier scattering for the ambipolar transport of optically generated carriers in a thin semiconductor slab

The ambipolar transport of an electron–hole–acoustic-phonon system in a semiconductor slab of some micrometers thickness is studied in an effective one-component model. Numerical solutions of the Boltzmann equation in relaxation-time approximation are given for different carrier-carrier scattering times ${\tau }_{c\mathrm{-}c}$. Surprisingly, the resulting profiles of hydrodynamic variables (density, average velocity, and carrier temperature) are found to sensitively depend on this parameter. In the limiting cases of very weak, i.e., ${\tau }_{c\mathrm{-}c}$ large compared with the carrier-phonon scattering time, or very strong carrier-carrier scattering, the profiles can be calculated to a good approximation in hydrodynamic models. In the latter case a nondiffusive velocity overshoot may occur. From the distribution function the line shape of the luminescence spectra is calculated as function of ${\tau }_{c\mathrm{-}c}$ and slab thickness.