Photoluminescence characterization of InAs/GaAs quantum dot bilayers

We have investigated the emission from InAs/GaAs quantum dots (QD) bilayer samples with different GaAs spacer thickness. For large spacers, one peak is observed, and the layers are independent. For small spacers, one peak is observed and the layers are then electronically coupled. For intermediate spacers (≈120 Å), two emission peaks are observed and these can be made coincident by tuning the amount of InAs deposited in the second layer. We present a technique using two different excitation wavelengths, which enables us to attribute the emission to each layer, and to show that the shifts are not due to electronic coupling. Moreover, resonant excitation shows that the wetting layers are also different in each layer. These results indicate that the presence of the first QD layer strongly influences the growth of the second one, leading to very different properties.