Femtosecond Luminescence Measurements In GaAs.

We report luminescence measurements in GaAs with femtosecond time resolution. This represents more than an order-of-magnitude improvement over previous luminescence measurements and allows us to study initial relaxation processes of photoexcited carriers. We show that the relaxation of photoexcited carriers to the band extrema is delayed by 750 fsec when the excitation density is reduced from 3 x 10(18) cm(-3) to 1 x 10(17) cm(-3). We have measured luminescence rise and decay curves at various photon energies ranging from 1.45 eV to 1.70 eV. These results are discussed in terms of carrier-carrier and carrier-phonon interactions.