Ultrafast optical nonlinearities of type II AlxGa1−xAs/AlAs multiple quantum wells

We present experimental studies of the transient optical nonlinearities near the direct band gap of type II AlxGa1−xAs/AlAs multiple quantum wells. The response of the optical nonlinearity at the band-gap excitonic transition is critically dependent on laser photon energy. A complete recovery of the bleached absorption in the lower part of the excitonic resonance with a picosecond time constant at room temperature occurs due to an enhanced collision broadening of the excitonic resonance after the fast spatial Γ–X transfer. Our results demonstrate that the intrinsic response of optical devices based on exciton nonlinearities can be much faster in type II structures as compared to type I structures.<squeeze;2p>