Use of Silicon Nanopillars Facilitated by New Fabrication Technology

Experts around the world are striving to implement quantum information technologies. A key way concerns light: Individual packets of light, also known as photons or light quanta, could transmit data both encrypted and efficiently tap-proof.

The researchers use an objective lens to test the light output of an array of silicon nanopillars on a chip. Image source: Helmholtz Center Dresden Rossendorf/Juan Baratech.

New photon sources are needed that emit individual light quanta in a controlled manner – and that on request. Only recently was it discovered that silicon is able to host sources of single photons with ideal properties for quantum communication. So far, little research has been published on how to integrate the sources into advanced photonic circuits.

A research team led by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has for the first time demonstrated a suitable production technology using silicon nanopillars, a chemical etching process followed by ion bombardment.

Silicon and single-photon sources in telecommunications have long been the missing link in accelerating the development of quantum communications through optical fibers. We have now created the necessary conditions for this.

dr Yonder Berencén, Head of Studies, Institute for Ion Beam Physics and Materials Research, Helmholtz Center Dresden Rossendorf

While single-photon sources have been fabricated in materials like diamonds, only silicon-based sources can produce light particles at the precise wavelength to propagate in optical fibers – a significant advantage for useful purposes.

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The scientists achieved this technical innovation by choosing a wet etch process – metal-assisted chemical etching (MacEtch) – instead of the traditional dry etch processes to machine the silicon on a chip. These typical approaches, which enable the formation of silicon photonic structures, use extremely reactive ions.

Due to radiation damage, these ions trigger light-emitting defects in the silicon. However, they are randomly distributed and add noise to the preferred optical signal. On the other hand, MacEtch does not create these errors – rather, the material is chemically etched away under a kind of metallic mask.

My dream is to integrate all the elementary building blocks from a single photon source to photonic elements to a single photon detector on a single chip and then connect many chips via commercial optical fibers into a modular quantum network.

dr Yonder Berencén, Head of Studies, Institute for Ion Beam Physics and Materials Research, Helmholtz Center Dresden Rossendorf

The goal: single-photon sources that are compatible with the fiber optic network

With the MacEtch technique, the scientists originally created the simplest form of a possible optical waveguide structure: silicon nanopillars on a chip. They then bombarded the completed nanopillars with carbon ions as they would a giant block of silicon, creating sources of photons that were implanted into the pillars.

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By using the novel etching technique, the size, surface density, and spacing of the nanopillars can be precisely controlled and adapted to advanced photonic circuits. Thousands of silicon nanopillars per square millimeter of the chip transmit and focus the light from the sources by regulating it vertically via the pillars.

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The diameter of the columns was varied by the scientists.

WWe had hoped that this would mean that we could do single defect creation on thin pillars and actually create a single photon source per pillar. It didn’t work perfectly the first time. In comparison, the dose of our carbon bombardment was too high for even the thinnest columns. But now it is only a small step to single photon sources.

dr Yonder Berencén, Head of Studies, Institute for Ion Beam Physics and Materials Research, Helmholtz Center Dresden Rossendorf

magazine reference

Hollenbach, M., et al. (2022) Metal-assisted chemically etched silicon nanopillars housing telecommunications photon emitters. Journal of Applied Physics.


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