Characterization of exciton states in coupled InAlAs/AlGaAs quantum dot pairs

We study the exciton states of vertically coupled InAlAs/AlGaAs self-assembled quantum dot (QD) pairs which were designed to have different wetting-layer edges in two QD layers. From a single QD pair, micro-photoluminescence demonstrates four exciton s levels as a result of interdot coupling. Consistent with theory, such a level can be split into four sub-levels. In general, 2-fold splitting is exhibited by the doublet under magnetic field. The doublet is of near-circular polarization in one side but of near-linear polarization in the other side. This abnormal behavior might be understood by heavy hole-light hole mixing. The other 2-fold splitting is observed by photoluminescence excitation measurement without magnetic field. This splitting is suggested resulting from the spatial asymmetry of the coupled QD pair. It is possible that these two split states are robust against magnetic field, and are selectively excited by using pump energy associated with different wetting layers.