Experts are working to implement quantum information technologies all over the world. One crucial route involves light. In the future, data could be transmitted that is both coded and practically tap proof using single light packages, also known as light quanta or photons.
Therefore, new photon sources that emit single light quanta in a controlled manner — and when needed — are desirable. It has only recently been found that silicon can support single-photon sources with characteristics suitable for quantum communication. But nobody has yet figured out how to incorporate the sources into contemporary photonic circuits.
Using silicon nanopillars, a team led by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has now demonstrated an appropriate production technique: Ion bombardment followed by chemical etching.
“Silicon and single-photon sources in the telecommunication field have long been the missing link in speeding up the development of quantum communication by optical fibers. Now we have created the necessary preconditions for it,”
said study leader Dr. Yonder Berencén of HZDR’s Institute of Ion Beam Physics and Materials Research.
Metal Assisted Chemical Etching
Depiction of the mechanism of metal assisted chemical etching of silicon.
The reduction of an oxidizing agent (in this case H2O2) is catalyzed at the surface of a noble metal nanoparticle (in this case gold). Because of this, holes (h+) are injected into the valence band of the silicon substrate. These holes weaken chemical bonds at the silicon/etching solution interface and thus dissolution of the substrate with HF takes place.
Credit: Galaktico
Despite the fabrication of single-photon sources in materials such as diamonds, only silicon-based sources produce light particles at the proper wavelength to populate optical fibers — a significant advantage for practical applications.
The method by which the researchers processed the silicon on a chip was wet etching, also known as MacEtch (metal-assisted chemical etching), as opposed to the more common dry etching methods. These common techniques make use of highly reactive ions to enable the construction of silicon photonic structures.
By damaging the silicon with radiation, these ions cause defects that emit light. They are dispersed at random, though, and add noise on top of the desired optical signal.
In contrast, defects are not produced during metal-assisted chemical etching; instead, the material is chemically removed while being covered by a kind of metallic mask.
Fiber-optic Network-compatible Single Photon Sources
Researchers first created silicon nanopillars on a chip, the most basic form of a potential light wave-guiding structure, using the MacEtch technique. As they would with a large silicon block, they then blasted the completed nanopillars with carbon ions, creating photon sources within the pillars.
The size, spacing, and surface density of the nanopillars can be precisely controlled and altered using the new etching method to make them compatible with contemporary photonic circuits. Thousands of silicon nanopillars per square millimetre chip conduct and bundle the light from the sources by directing it vertically through the pillars.
Why did the researchers vary the diameter of the pillars?
“We had hoped this would mean we could perform single defect creation on thin pillars and actually generate a single photon source per pillar. t didn’t work perfectly the first time. By comparison, even for the thinnest pillars, the dose of our carbon bombardment was too high. But now it’s just a short step to single photon sources,”
explained Berencén.
The team is already putting a lot of effort into this step because the new technique has also sparked a competition for potential future applications.
“My dream is to integrate all the elementary building blocks, from a single photon source via photonic elements through to a single photon detector, on one single chip and then connect lots of chips via commercial optical fibers to form a modular quantum network,”
Berencén concluded.
References:
Michael Hollenbach et al, Metal-assisted chemically etched silicon nanopillars hosting telecom photon emitters, Journal of Applied Physics 132, 033101 (2022)
Michael Hollenbach, Yonder Berencén, Ulrich Kentsch, Manfred Helm, and Georgy V. Astakhov, Engineering telecom single-photon emitters in silicon for scalable quantum photonics, Opt. Express 28, 26111-26121 (2020)
