Optical anisotropy in vertically coupled quantum dots

We have studied the polarization of surface and edge-emitted photoluminesce nce (PL) from structures with vertically coupled In0.5Ga0.5As/GaAs quantum dots (QD's) grown by molecular beam epitaxy. The PL polarization is found t o be strongly dependent on the number of stacked layers. While single-layer and 3-layer structures show only a weak TE polarization, it is enhanced fo r 10-layer stacks. The 20-layer stacks additionally show a low-energy side- band of high TE polarization, which is attributed to laterally coupled QD's forming after the growth of many layers by lateral coalescence of QD's in the upper layers. While in the single, 3- and 10-layer stacks, both TE pola rized PL components an stronger than the TM component, the [110] TE compone nt is weaker than the TM component in the 20-layer stack. This polarization reversal is attributed to an increasing vertical coupling with increasing layer number due to increasing dot size. [S0163-1829(99)05747-1].