Determination of intervalley scattering rates in GaAs by subpicosecond luminescence spectroscopy

We report a slow rise of luminescence in GaAs following subpicosecond photoexcitation and show that it results from a slow return of electrons from the L to the \ensuremath{\Gamma} valley. By fitting our data with an ensemble Monte Carlo calculation, we determine the \ensuremath{\Gamma}-L deformation potential to be (6.5\ifmmode\pm\else\textpm\fi{}1.5)\ifmmode\times\else\texttimes\fi{}${10}^{8}$ eV/cm. We show that the electrons returning to the \ensuremath{\Gamma} valley act as a source of heating for the photoexcited plasma. We further show the importance of electron-electron scattering and inadequacy of a simple phonon-cascade model, even at a density as low as 5\ifmmode\times\else\texttimes\fi{}${10}^{16}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$.