EFFICIENT INTERSUBBAND SCATTERING VIA CARRIER-CARRIER INTERACTION

Using femtosecond resonant luminescence, we have measured the intersub band scattering rate of electrons in wide GaAs quantum wells at very l ow excitation densities. Even when the spacing be tween the first two electron subbands is smaller than the LO phonon energy, we observe tha t intersubband scattering is a subpicosecond process, much faster than previously measured or anticipated. Our experimental results are in p erfect agreement with Monte Carlo calculations, which show that carrie r-carrier interaction is responsible for the ultrafast transitions.