Anomalously Large Stokes and anti-Stokes Real Space Charge Transfer Between Quantum Wells Separated by Thick Alloy Barriers: Beyond the Mean Field Approach

Anomalously large real space charge transfer through thick alloy barriers in GaAs asymmetric double quantum wells is studied by photoluminescence excitation. This inter-well excitonic transfer is very large when the barrier is the Al_0.3Ga_0.7As alloy, but disappears when the barrier is GaAs/AlAs digital alloy with an equivalent x=0.28. Furthermore, for a shallow InGaAs/GaAs/InGaAs ADQW, it largely disappears despite the lower barrier height. These results suggest that the inhomogeneities of the atomic arrangment of Ga and Al in the alloy, which is a strong function of x, might be responsible for this transfer. This picture is qualitatively supported by quantum mechanical calculation in three dimensions whose scopes reach beyond the mean field approach. We, furthermore, presents the existence of an anti-Stokes transfer from the wide well to the narrow well, and discuss its origin.