Manipulating the energy levels of semiconductor quantum dots

Artificial atoms with up to five well-defined electronic shells are fabricated using self-assembled quantum dots (QD’s) grown by molecular-beam epitaxy. State-filling spectroscopy of the zero-dimensional transitions between confined electrons and holes demonstrates that the energy levels are readily tunable. One to five confined levels, with an interlevel energy spacing between 25 and 90 meV, are obtained by adjusting the growth temperature or with post growth annealings. The uniformity and reproducibility of InAs/GaAs QD’s are optimized by adjusting growth parameters affecting the evolution and the equilibrium shape of the QD’s: the amount of strained material deposited, and the annealing time following the InAs deposition. Well-defined excited states are also obtained with stacked layers of vertically self-assembled QD’s.