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 Γ valley. By fitting our data with an ensemble Monte Carlo calculation, we determine the Γ-L deformation potential to be (6.5±1.5)×${10}^8$ eV/cm. We show that the electrons returning to the Γ 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×${10}^{16}$ ${\mathrm{cm}}^{\mathrm{-}3}$.

• Received 6 July 1987

DOI:https://doi.org/10.1103/PhysRevLett.59.2222