The response of quantum dots to an electric field can be greatly enhanced by forming quantum dot molecules: two InAs quantum dots are stacked on top of each other, separated by a GaAs barrier a few nanometers thick. The pair of dots can be controlled by applied voltage such that they share a single hole [4]. Normally the hole energy levels of the two dots are much different (because of differences in structure), tunneling between dots is negligible, and the dot states are atomiclike. However, when the two dots are tuned by an applied electric field to have the same hole energy, resonant tunneling of the hole becomes significant, and the state of the hole becomes molecularlike. The two atomiclike states combine to form a molecular “bonding” orbital with enhanced wave function in the barrier, and a molecular “antibonding” orbital with suppressed amplitude in the barrier.
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