Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Atomic-scale mapping of quantum dots formed by droplet epitaxy

Abstract

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.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Prices may be subject to local taxes which are calculated during checkout

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.

Similar content being viewed by others

References

  1. Yoffe, A. D. Semiconductor quantum dots and related systems: electronic, optical, luminescence and related properties of low dimensional systems. Adv. Phys. 50, 1–208 (2001).

    Article  CAS  Google Scholar 

  2. Borovitskaya, E. & Shur, M. S. Quantum dots. Sel. Top. Electr. Syst. 25 (2002).

  3. Biolatti, E., Iotti, R. C., Zanardi, P. & Rossi, F. Quantum information processing with semiconductor macroatoms. Phys. Rev. Lett. 85, 5647–5650 (2000).

    Article  CAS  Google Scholar 

  4. Geller, M. et al. 106 years extrapolated hole storage time in GaSb/AlAs quantum dots, Appl. Phys. Lett. 91, 242109 (2007).

    Article  Google Scholar 

  5. Grätzel, M. Photoelectrochemical cells. Nature 414, 338–344 (2001).

    Article  Google Scholar 

  6. Robel, I., Subramanian, V. Kuno, M. & Kamat, P. V. Quantum dot solar cells. Harvesting light energy with CdSe nanocrystals molecularly linked to mesoscopic TiO2 films. J. Am. Chem. Soc. 128, 2385–2393 (2006).

    Article  CAS  Google Scholar 

  7. Koguchi, N., Ishige, K. & Takahashi, S. New selective molecular-beam-epitaxial growth method for direct formation of GaAs quantum dots. J. Vac. Sci. Technol. B 11, 787–790 (1993).

    Article  CAS  Google Scholar 

  8. Shusterman, S., Paltiel, Y., Sher A., Ezersky & Rosenwaks, Y. High-density nanometer-scale InSb dots formation using droplet heteroepitaxial growth by MOVPE, J. Cryst. Growth 291, 363–369 (2006).

    Article  CAS  Google Scholar 

  9. Sablon, K. A., Lee, J. H., Wang, Z., Shultz, J. H. & Salamo, G. J. Configuration control of quantum dot molecules by droplet epitaxy. Appl. Phys. Lett. 92, 203106 (2008).

    Article  Google Scholar 

  10. Shusterman, S. et al. Nanoscale mapping of strain and composition in quantum dots using Kelvin probe force microscopy. Nano Lett. 7, 2089–2093 (2007).

    Article  CAS  Google Scholar 

  11. Wang, Y. et al. Real-time X-ray studies of gallium nitride nanodot formation by droplet heteroepitaxy. J. Appl. Phys. 102, 073522 (2007).

    Article  Google Scholar 

  12. Yacoby, Y. et al. Direct determination of epitaxial interface structure in Gd2O3 passivation of GaAs. Nature Mater. 1, 99–101 (2002).

    Article  CAS  Google Scholar 

  13. Kumah, D. P. et al. Resonant coherent Bragg rod analysis of strained epitaxial heterostructures. Appl. Phys. Lett. 93, 081910 (2008).

    Article  Google Scholar 

  14. Cionca, C. N. et al. Interfacial structure, bonding and composition of InAs and GaSb thin films determined using coherent Bragg rod analysis. Phys. Rev. B 75, 115306 (2007).

    Article  Google Scholar 

  15. Eaglesham, D. J. & Cerullo, M. Dislocation-free Stranski-Krastanow growth of Ge on Si (100). Phys. Rev. Lett. 64, 1943–1946 (1990).

    Article  CAS  Google Scholar 

  16. He, L. X., Bester G. & Zunger, A. Strain-induced interfacial hole localization in self-assembled quantum dots: Compressive InAs/GaAs versus tensile InAs/InSb. Phys. Rev. B 70, 235316 (2004).

    Article  Google Scholar 

  17. Pryor, C. J. & Pistol, M. J. Band-edge diagrams for strained iiiv semiconductor quantum wells, wires, and dots. Phys. Rev. B 72, 205311 (2005).

    Article  Google Scholar 

  18. Joe, Y. S., Ikeler, D. S., Cosby, R. M., Satanin, A. M. & Kim, C. S. Characteristics of transmission resonance in a quantum-dot superlattice. J. Appl. Phys. 88, 2704–2708 (2000).

    Article  CAS  Google Scholar 

  19. Johansson, J. et al. Structural properties of (111)B-oriented iii-v nanowires. Nature Mater. 5, 574–580 (2006).

    Article  CAS  Google Scholar 

  20. Wang, Zh. M., Liang, B. L., Sablon, K. A. & Salamo, G. J. Nanoholes fabricated by self-assembled gallium nanodrill on GaAs (100). Appl. Phys. Lett. 90, 113120 (2007).

    Article  Google Scholar 

  21. Koguchi, N. & Ishige, K. Growth of GaAs epitaxial microcrystals on an S-terminated GaAs substrate by successive irradiation of Ga and As molecular beams. Jpn. J. Appl. Phys. 32, 2052–2058 (1993).

    Article  CAS  Google Scholar 

  22. Timm, R. et al. Structure of InAs/GaAs quantum dots grown with Sb surfactant. Physica E 32, 25–28 (2006).

    Article  CAS  Google Scholar 

  23. Shusterman, S., Raizman A. & Paltiel Y. Narrow gap nano-dots grown in the heteroepitaxial droplets mode. Infrared Phys. Technol. (in the press).

  24. Yacoby, Y. et al. Structural changes induced by metal electrode layers on ultrathin BaTiO3 films. Phys. Rev. B 77, 195426 (2008).

    Article  Google Scholar 

  25. Molina, S. I. et al. High resolution electron microscopy of GaAs capped GaSb nanostructures. Appl. Phys. Lett. 94, 043114 (2009).

    Article  Google Scholar 

  26. Fry, P. W. et al. Inverted electron-hole alignment in InAs-GaAs self-assembled quantum dots. Phys. Rev. Lett. 84, 734–736 (2000).

    Article  Google Scholar 

  27. Yacoby Y. et al. Direct structure determination of systems with two-dimensional periodicity. J. Phys. Condens. Mat. 12, 3929–3938 (2000).

    Article  CAS  Google Scholar 

  28. Elser, V. Solution of the crystallographic phase problem by iterated projection. Acta Cryst. A 59, 201–209 (2003).

    Article  Google Scholar 

  29. Stahn, J., Möhle, M. & Pietsch, U. Comparison of experimental and theoretical structure amplitudes and valence charge densities of GaAs. Acta Crystallographica B 54, 231–239 (1998).

    Article  Google Scholar 

Download references

Acknowledgements

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.

Author information

Authors and Affiliations

Authors

Contributions

All authors contributed equally to the work.

Corresponding author

Correspondence to Roy Clarke.

Supplementary information

Supplementary information

Supplementary information (PDF 413 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Kumah, D., Shusterman, S., Paltiel, Y. et al. Atomic-scale mapping of quantum dots formed by droplet epitaxy. Nature Nanotech 4, 835–838 (2009). https://doi.org/10.1038/nnano.2009.271

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nnano.2009.271

This article is cited by

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing