Carrier and screening dynamics in strained [111]-oriented multiple quantum wells

We have time-resolved the piezoelectric optical nonlinearities of a strained, [111]-oriented InGaAs/GaAs multiple quantum well p-i-n structure. By monitoring the temporal evolution of the excitonic absorption spectrum, we follow the photogenerated carriers as they drift to form the space-charge field responsible for screening the piezoelectric field. From the carrier dynamics, we can separate the contribution of in-well screening from that of the long-range screening associated with carriers that have escaped the wells. We have determined that in narrow quantum wells, in-well screening is smaller than long-range screening and that in-well screening is obscured by the concurrent onset of strong bleaching.