New photon sources are required that emit single light quanta in a controlled fashion and on demand. Only recently has it been discovered that silicon can host sources of single-photons with properties suitable for quantum communi­cation. So far, however, no-one has known how to integrate the sources into modern photonic circuits. For the first time, a team led by the Helmholtz-Zentrum Dresden-Rossen­dorf (HZDR) has now presented an appropriate production techno­logy using silicon nano­pillars: a chemical etching method followed by ion bombard­ment.

“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,” explains Yonder Berencén of HZDR’s Institute of Ion Beam Physics and Materials Research who led the current study. Although single-photon sources have been fabricated in materials like diamonds, only silicon-based sources generate light particles at the right wavelength to proli­ferate in optical fibers – a consi­derable advantage for practical purposes.

The researchers achieved this technical break­through by choosing a wet etching technique rather than the conventional dry etching techniques for processing the silicon on a chip. These standard methods, which allow the creation of silicon photonic structures, use highly reactive ions. These ions induce light-emitting defects caused by the radiation damage in the silicon. However, they are randomly distri­buted and overlay the desired optical signal with noise. Metal-assisted chemical etching, on the other hand does not generate these defects – instead, the material is etched away chemically under a kind of metallic mask.

Using this MacEtch method, researchers initially fabri­cated the simplest form of a potential light wave-guiding structure: silicon nanopillars on a chip. They then bombarded the finished nano­pillars with carbon ions, just as they would with a massive silicon block, and thus generated photon sources embedded in the pillars. Employing the new etching technique means the size, spacing, and surface density of the nano­pillars can be precisely controlled and adjusted to be compatible with modern photonic circuits. Per square milli­meter chip, thousands of silicon nanopillars conduct and bundle the light from the sources by directing it vertically through the pillars.

The researchers varied the diameter of the pillars because “we had hoped this would mean we could perform single defect creation on thin pillars and actually generate a single photon source per pillar” explains Berencén. “It 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.”

A step on which the team is already working inten­sively because the new technique has also unleashed something of a race for 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,” says Berencén. (Source: HZDR)

Reference: M. Hollenbach et al.: Metal-assisted chemically etched silicon nanopillars hosting telecom photon emitters, J. Appl. Phys. 132, 033101 (2022); DOI: 10.1063/5.0094715

Link: Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf HZDR, Dresden, Germany