Abstract
The tunneling coupling in three vertically stacked (In,Ga)As/GaAs
quantum rings is investigated. With increasing inter-ring separation
(d), we find that the nonuniform strain results into a crossing of the
lowest-energy electron states. Strain is also responsible for an
increase in the ground electron energy above the level in the single
quantum ring. The ground hole energy level exhibits decrease when d
decreases, which is typical for antibonding states in an unstrained
structure. These effects lead to a local maximum in the dependence of
the ground-state exciton energy on d. Our theoretical results compare
well with recent photoluminescence measurements but deviate considerably
from the calculations for flat bands in quantum-ring molecules. We
conclude that the nonuniform character of the strain distribution gives
rise to a peculiar exciton hybridization in self-assembled quantum-ring
molecules.
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