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Optical emission from a charge-tunable quantum ring

Abstract

Quantum dots or rings are artificial nanometre-sized clusters that confine electrons in all three directions. They can be fabricated in a semiconductor system by embedding an island of low-bandgap material in a sea of material with a higher bandgap. Quantum dots are often referred to as artificial atoms because, when filled sequentially with electrons, the charging energies are pronounced for particular electron numbers1,2,3; this is analogous to Hund's rules in atomic physics. But semiconductors also have a valence band with strong optical transitions to the conduction band. These transitions are the basis for the application of quantum dots as laser emitters4, storage devices5,6,7 and fluorescence markers8. Here we report how the optical emission (photoluminescence) of a single quantum ring changes as electrons are added one-by-one. We find that the emission energy changes abruptly whenever an electron is added to the artificial atom, and that the sizes of the jumps reveal a shell structure.

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Figure 1: The semiconductor device for charging quantum rings with electrons.
Figure 2: A colour-scale plot of the photoluminescence (PL) versus gate voltage at 4.2 K.
Figure 3: Photoluminescence from a single quantum ring for different charge states.
Figure 4: PL of a single quantum ring in the transition from one charge state to the next.

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Acknowledgements

We thank J. P. Kotthaus and N. D. Drew for discussions. This work was supported by the Deutsche Forschungsgemeinschaft and by QUEST, an NSF Science and Technology Center.

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Correspondence to R. J. Warburton.

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Warburton, R., Schäflein, C., Haft, D. et al. Optical emission from a charge-tunable quantum ring. Nature 405, 926–929 (2000). https://doi.org/10.1038/35016030

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