)B substrates

In0.45Ga0.55As/GaAs multistacking quantum dot (QD) structures were fabricated on a GaAs (n11)B (n=2–4) substrate by metalorganic vapor-phase epitaxy. QDs spontaneously aligned in the [0 1 1] direction were observed on stacked QDs, whereas QDs were randomly distributed in the initial In0.45Ga0.55As layer growth. The formation mechanism of this self-alignment was studied by changing the number of In0.45Ga0.55As/GaAs multilayers and crystallographic arrangement. Photoluminescence spectra showing clear polarization dependence indicate carrier coupling in the QD arrays. This growth technique results in spontaneously aligned InGaAs QDs without any preprocessing technique prior to growth.