Initial Relaxation of Photoexcited Carriers in GaAs and GaAs Quantum Wells Under Subpicosecond Excitation.

After excitation by a subpicosecond pulse, we observe a very slow rise of the luminescence both in GaAs and GaAs quantum well. By comparing the results in GaAs and InP, we show that the slow rise in GaAs and GaAs quantum wells is due to the slow return of the electrons from the L to the GAMMA valley. Our results show the importance of electron-electron scattering and the inadequacy of a simple phonon cascade model at densities as low as 5x10 sup (16) cm sup (-3).