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Atomic-scale mapping of quantum dots formed by droplet epitaxy


Quantum dots (QDs) have applications in optoelectronic devices1,2, quantum information processing3,4 and energy harvesting5,6. Although the droplet epitaxy fabrication method7,8,9 allows for a wide range of material combinations to be used, little is known about the growth mechanisms involved10,11. Here we apply direct X-ray methods12,13,14 to derive sub-ångström resolution maps of QDs crystallized from indium droplets exposed to antimony, as well as their interface with a GaAs (100) substrate. We find that the QDs form coherently15 and extend a few unit cells below the substrate surface. This facilitates a droplet–substrate exchange of atoms, resulting in core–shell structures that contain a surprisingly small amount of In. The work provides the first atomic-scale mapping of the interface between epitaxial QDs and a substrate, and establishes the usefulness of X-ray phasing techniques for this and similar systems.

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Figure 1: Group iiiv QDs formed by In-droplet epitaxy on a GaAs (100) substrate.
Figure 2: Electron density profiles measured normal to the substrate surface through lines of group iii (top) and group v (bottom) sites in the zinc-blende structure.
Figure 3: Determining lateral strain relaxation from the in-plane folded electron density.


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The work was supported by the US National Science Foundation under Grant DMR-0606048. Synchrotron radiation facilities at the Advanced Photon Source were supported by DOE Contract No. DE-AC02-06CH11357. The authors are grateful to N. Husseini for useful discussions and comments.

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Correspondence to Roy Clarke.

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Kumah, D., Shusterman, S., Paltiel, Y. et al. Atomic-scale mapping of quantum dots formed by droplet epitaxy. Nature Nanotech 4, 835–838 (2009).

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