Fast escape of photocreated carriers out of shallow quantum wells

We report that at room temperature the field-induced escape of photogenerated carriers out of shallow GaAs/AlxGa1−xAs multiple quantum wells is as fast as for pure GaAs of the same thickness, if the value of x does not exceed 0.04. Our experimental findings can be explained by assuming that carriers are efficiently scattered into the unconfined barrier states by absorption of a LO phonon, as long as the effective barrier height is less than the LO-phonon energy. The application of shallow quantum wells with x≤0.04 in self-electro-optic effect devices, providing not only strong excitonic electroabsorption but also fast sweep-out times at small biases, should lead to shorter switching times.