Excitation transfer in novel self-organized quantum dot structures

We report on studies of excitation transfer processes in vertically self-or ganized pairs of unequal-sized quantum dots (QDs), created in InAs/GaAs bil ayers having differing InAs deposition amounts in the first (seed) and subs equent layer. The former and latter enable independent control, respectivel y, of the density and the site distribution of the second layer QDs, This a pproach allows us to enhance the average volume and improve the uniformity of InAs QDs, resulting in low-temperature photoluminescence at 1.028 eV wit h a linewidth of 25 meV for 1.74 ML (seed)/3.00 ML InAs stacking. The optic al properties of the formed pairs of unequal-sized QDs with clearly discern ible ground-stare transition energy depend on the spacer thickness and comp osition. Photoluminescence results provide evidence for nonresonant energy transfer from the smaller QDs in the seed layer to the larger QDs in the se cond layer in such asymmetric QD pairs. Transfer times down to 20 ps (36 ML GaAs spacer) are estimated, depending exponentially on the GaAs spacer thi ckness. (C) 1999 Academic Press.