Schemes of structure geometry, required Sb concentration profile, and expected band edge profile at cross section in QD axis.
Cross section HRTEM image, viewed along the  zone axis showing the vertically correlated combined QDs (structure type A5) separated by the GaAsSb barrier.
Calculated band alignment in the axis of vertically correlated combined InAs and GaAs0.76Sb0.24 QDs, separated by triangular GaAsSb barrier with graded Sb content from 10% to 24% (fit of sample A7). The insets demonstrate maps of the calculated valence (left scale) and conduction (right scale) band edge energies for InAs and GaAs0.76Sb0.24 QDs in (100) cross section, the corresponding values of band edge energies along QD axis are plotted in the graph on the left.
(a) PL spectra of vertically correlated combined InAs and GaAsSb QDs separated by 3 nm thick triangular GaAsSb barrier with graded Sb concentration for different GaAsSb QD composition. The inset shows the dependence of the ground and the excited state PL maxima on the composition of GaAsSb QDs. (b) Comparison of PL spectra of samples A7 and B measured with 100% excitation intensity (on top) and PL spectra of sample B (without triangular barrier) for two different excitation intensities (at the bottom). The blueshift of the ground state maximum of sample B with increased excitation intensity is a proof of the type-II band alignment. (The fine structure on sample B PL spectra in vicinity of 1400 nm is caused by the water vapor absorption.)
Photoluminescence of two samples C1 and C2 with different thickness of GaAsSb QD region. The PL maximum of sample C2 is redshifted with eight times lower intensity, since only a part of the biggest InAs QDs has the type-I band alignment with QD PL (see schematic drawings).
Parameters of the structure estimated from the NextNano++ simulation.
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