Looking for Color Centers in SiC

Green silicon carbide substrate at the bottom with the graphene layer on top irradiated by protons, generating a luminescent defect in the SiC crystal. (Source: M. Rühl, FAU)

Silicon carbide, a material known for its toughness with appli­cations from abrasives to car brakes, to high-tempera­ture power electronics, has enjoyed renewed interest for its potential in quantum tech­nology. Its ability to house optically excitable defects, called color centers, has made it a strong candidate material to become the building block of quantum computing. Now, a group of german researchers at the Univer­sity of Nurem­berg-Erlangen FAU has created a list of recipes physicists can use to create specific types of defects with desired optical proper­ties in SiC.

In one of the first attempts to systema­tically explore color centers, the group used proton irra­diation techniques to create the color centers in silicon carbide. They adjusted proton dose and tempera­ture to find the right conditions that reliably produce the desired type of color center. Atomic defects in the lattice of SiC crystals create color centers that can emit photons with unique spectral signatures. While some materials considered for quantum computing require cryo­genically low tempera­tures, color centers in SiC can emit at room tempera­ture. As the push to create increa­singly smaller devices continues into atom-scale sensors and single-photon emitters, the ability to take advantage of existing SiC inte­grated circuit tech­nology makes the material a standout candidate.

To create the defects, Michael Krieger and his col­leagues bombarded SiC samples with protons. The team then let the SiC go through a heating phase called annealing. „We’re doing a lot of damage to these crystals,“ Krieger said. „However, during annealing, the crystal structure recovers, but defects are also formed – some of them are the desired color centers.“ To ensure that their recipes are compatible with usual semi­conductor tech­nology, the group opted to use proton irra­diation. Moreover, this approach doesn’t require electron acce­lerators or nuclear reactors like other techniques used to create color centers.

The data from using different doses and annealing tempera­tures showed that producing defects in SiC follows a pattern. Initially protons generate predo­minantly silicon vacancies in the crystal, then those vacancies sequen­tially transform into other defect complexes. Studying the defects’ low-tempera­ture photo­lumines­cence spectra led the team to discover three previously unreported signa­tures. The three tempera­ture-stable (TS) lines were shown to correlate with proton dose and annealing tempera­ture. Krieger said these TS lines have exciting pro­perties and further research is already going on as the group hopes to utilize and control those defects for use in SiC-based quantum tech­nology devices. (Source: AIP)

Reference: M. Rühl et al.: Controlled generation of intrinsic near-infrared color centers in 4H-SiC via proton irradiation and annealing, Appl. Phys. Lett. 113, 122102 (2018); DOI: 10.1063/1.5045859

Link: Chair of Applied Physics, Dept. of Physics, University of Erlangen-Nürnberg FAU, Erlangen, Germany

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