Evidence of coupling between InAs self-assembled quantum dots in thin GaAs buffer layer

We have studied the optical properties of two layers of InAs self-assembled quantum dots (QDs). The QDs were separated by a GaAs barrier with thickness varied from 2.5 to 10 nm. All samples exhibited double peaks from low-temperature photoluminescence spectra. The energy difference between two peaks shows that the origin of the double peaks is different for each sample. In case of the thin barrier thickness, the double peaks are due to the coupling of the ground states of lower and upper dots. In the thick barrier case, the double peaks originate from the ground and excited states because the barrier is thick enough to separate the double QDs.