Excitation transfer in self-organized asymmetric quantum dot pairs

Excitation transfer processes within self-organized quantum dot (QD) pairs in bilayer InAs/GaAs QD samples are investigated. QDs in samples with a 1.74-ML InAs seed layer and a 2.00 ML InAs second layer are found to self-organize in pairs of unequal sized QDs with clearly discernible ground-state transition energy. Photoluminescence (PL) and PL excitation results for such asymmetric QD pairs provide evidence for nonresonant energy transfer from the smaller QDs in the seed layer to the larger QDs in the second layer. Variations in the optical behavior as a function of the spacer thickness and composition are attributed to the barrier-dependent tunnel probability. Tunneling times down to 20 ps (36 ML GaAs spacer) are estimated, depending exponentially on the GaAs spacer thickness.