Recent experimental measurements, without any theoretical guidance, showed
that isotropic polarization response can be achieved by increasing the number
of QD layers in a QD stack. Here we analyse the polarization response of
multi-layer quantum dot stacks containing up to nine quantum dot layers by
linearly polarized PL measurements and by carrying out a systematic set of
multi-million atom simulations. The atomistic modeling and simulations allow us
to include correct symmetry properties in the calculations of the optical
spectra: a factor critical to explain the experimental evidence. The values of
the degree of polarization (DOP) calculated from our model follows the trends
of the experimental data. We also present detailed physical insight by
examining strain profiles, band edges diagrams and wave function plots.
Multi-directional PL measurements and calculations of the DOP reveal a unique
property of InAs quantum dot stacks that the TE response is anisotropic in the
plane of the stacks. Therefore a single value of the DOP is not sufficient to
fully characterize the polarization response. We explain this anisotropy of the
TE-modes by orientation of hole wave functions along the [-110] direction. Our
results provide a new insight that isotropic polarization response measured in
the experimental PL spectra is due to two factors: (i) TM[001]-mode
contributions increase due to enhanced intermixing of HH and LH bands, and (ii)
TE[110]-mode contributions reduce significantly due to hole wave function
alignment along the [-110] direction. We also present optical spectra for
various geometry configurations of quantum dot stacks to provide a guide to
experimentalists for the design of multi-layer QD stacks for optical devices.
Our results predict that the QD stacks with identical layers will exhibit lower
values of the DOP than the stacks with non-identical layers.Comment: 10 pages, 7 figures, and 1 tabl
