Artificial molecules are studied using coupled quantum-dot (QD) ensembles with well-defined electronic shells. The coupling strength between the zero-dimensional states is varied by changing the distance between two layers of stacked self-assembled InAs/GaAs QDs. For strongly coupled QDs grown with a 4 nm spacer, state-filling spectroscopy reveals a shift of the QD symmetric state to lower energies by ∼23 meV. The wetting layer states are also strongly coupled because of the shallow confinement, resulting in a redshift of its symmetric state by ∼26 meV.
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25.
The spacer thickness d is related to the actual barrier thickness t for the QD by Also the effective QD width is the sum of the WL thickness plus h, and so using 1.25 nm for the QD width and a WL thickness of 0.54 nm gives for the QDs indium flushed at 3.0 nm.
26.
In less than half of the TEM images we have studied, a slight vertical misalignment of the stacked QDs can sometimes be observed as in Fig. 4(a). It does not appear to be correlated with the spacer thickness, but might change the entanglement of the coupled states.
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