Tuning of the electronic levels in vertically stacked InAs/GaAs quantum dots using crystal growth kinetics

We investigate tuning of the ground state energy levels in a pair of strain coupled quantum dot layers by changing the growth conditions for each layer. The shapes of the islands are analyzed before capping using atomic force microscopy. We study the effects of strain fields and In segregation on island nucleation, and find that the island shape in the second quantum dot layer is highly dependent on the dot density. Photoluminescence (PL) and micro-PL measurements are used to find growth conditions that provide for near matching of the ground transition energies of a quantum dot pair. We find that even if a large ensemble of vertically stacked quantum dot pairs yields a single PL peak, we are unable to obtain single pairs with identical ground state energies in the micro-PL spectra. Under optimal conditions the two dots differ by approximate to10 meV for a distance of 120 Angstrom between the quantum dot layers. (C) 2003 Elsevier Science B.V. All rights reserved.