Nanopyramids: Places of (Un)Rest for Light

Dr. Elisabeth Zuber-Knost
Press Officer

Kaiserstraße 12
76131 Karlsruhe, Germany
Phone: +49 721/608-2089
Fax: +49 721/608-3658

The Egyptian pyramids were intended to safely enclose the deceased pharaohs and to enable them to enter a new state. At the Karlsruhe Institute of Technology (KIT), working groups headed by Dr. Michael Hetterich and Professor Heinz Kalt have now developed pyramids of just several hundred nanometers in height (1 nm = 1 millionth of a millimeter). In these pyramids laser light interacts with so-called quantum dots.

Excited by the energy of the laser light, the quantum dots emit light within a certain range of wavelengths. In the pyramid which consists of the semiconductor compound gallium arsenide, this “new” light is “enclosed” and emitted again after a certain period of time has passed. The pyramid itself stands on a special mirror. In combination with the four sides of the pyramid, it reflects light such that it is confined inside the structure. Certain light waves overlap and amplify one another - a phenomenon known as resonance. Components using resonance-based quantum optical effects might be applied in the future to manipulate light. Thus, they may serve as a technical basis for novel quantum computers that would work much faster and more efficiently than today’s computers in certain fields (Appl. Phys. Lett. 90, 161104 (2007)).

To produce the pyramids, the researchers at the Center for Functional Nanostructures (CFN) of the KIT combined two techniques. By molecular beam epitaxy, they applied single layers of material only a few hundred atomic diameters in thickness.

Subsequently, the sample was immersed in a solution of phosphoric acid, hydrogen peroxide, and water, which etched off the individual layers to a variable degree. The mixing ratio of the ingredients determined the inclination of the sides of the pyramid. But it is their interior that is decisive for the functionality of these structures: Quantum dots consisting of a few thousand atoms of a different material are incorporated into the pyramids and specifically disturb the homogeneous crystal lattice of the gallium arsenide. When they are excited by laser light, they emit light of a different wavelength. The optical resonator enhances the light-matter interaction and increases the yield of light emitted at certain wavelengths.

Other optical resonators are still superior to the Karlsruhe nanopyramids in some respects. “But the new manufacturing process allows us to more specifically alter their geometry and their structure. Hence, their properties may be controlled much better compared to structures known so far,” explains the physicist Matthias Karl, member of the team headed by Professor Kalt. He also sees the combination of pyramids in groups as a rather promising option to create coupled structures which would be particularly interesting for applications in quantum information processing. It appears that this potential was also recognized by the renowned scientific journal “Nature Photonics”, which presented the work carried out in Karlsruhe in its June edition under “News & Views”.

The Center for Functional Nanostructures (CFN) will be part of the KIT NanoMikro Center that is planned to be founded by January 01, 2008.

For details, please contact
DFG-Centrum für Funktionelle Nanostrukturen (CFN)

Dr. Gerd König
Public Relations

Wolfgang-Gaede-Str. 1
76131 Karlsruhe, Germany
Phone: +49 721 608-3409
Fax: +49 721 608-8496

E-mail

http://www.cfn.uni-karlsruhe.de/

Photos

All photos, black and white or colored, are available on the website of the CFN:

References

• Weber, F.M et al.. Optical modes in pyramidal GaAs microcavities. Appl. Phys. Lett. 90, 161104 (2007)

• Pyramidal resonators. Nature Photonics 1, 317 (2007)