Silicon-On-Insulator Achieves Coupled Colour Centre Formation for Photon Sources

Scientists are increasingly focused on harnessing colour centres in silicon as a pivotal technology for on-chip photonic integration. Arnulf J. Snedker-Nielsen, David R. Gongora, and Magnus L. Madsen, from the NNF Quantum Computing Programme at the Niels Bohr Institute, University of Copenhagen, alongside colleagues including Christiansen, Piehorsch, Augustesen et al., detail a crucial investigation into generating these centres within silicon-on-insulator devices. Their research, published today, significantly advances the field by revealing the complex interplay between device fabrication processes and colour centre formation , identifying optimal parameters for creating stable, previously unobserved optical signals. This understanding is vital for realising scalable quantum technologies, including single-photon sources and multi-spin registers, paving the way for more powerful photonic integrated circuits.

Their research, published today, significantly advances the field by revealing the complex interplay between device fabrication processes and colour centre formation, identifying optimal parameters for creating stable, previously unobserved optical signals. This understanding is vital for realising scalable quantum technologies, including single-photon sources and multi-spin registers, paving the way for more powerful photonic integrated circuits.

Colour Centre Formation in Silicon-on-Insulator Devices

Scientists have demonstrated a significant advance in the creation of colour centres in silicon-on-insulator (SOI) devices, paving the way for scalable quantum photonic technologies. This research details the generation of multiple types of colour centres, including the T, I, M, C, G, and W centres, and meticulously examines how device development processes impact their formation. The team achieved precise control over these quantum emitters by investigating the effects of thermal annealing and nanofabrication steps, crucial for building photonic integrated circuits. This study reveals coupled dynamics between different colour centres, identifying optimal parameters for annealing processes and highlighting the sensitivity to both duration and nanofabrication procedures.
Experiments show that the formation of these colour centres is not independent; rather, their creation is intertwined, with the activation, suppression, and revival of certain defects dependent on annealing temperature. Detailed parameter scans were performed, varying both temperature, ranging from 200 to 600°C, and annealing time, from 30 to 600 seconds, to map these complex relationships. The research establishes optimised annealing parameters and fabrication procedures for colour centre formation in SOI, often differing from previously reported values in the literature. This optimisation is critical for achieving high densities of stable, optically-active defects.

Furthermore, the study unveils stable optical signals originating from previously unidentified colour centres in silicon, expanding the palette of potential quantum emitters available for technological applications. Researchers employed commercially available 220nm SOI wafers with resistivity ≥3000 Ωcm, utilising ion implantation of carbon and hydrogen, followed by thermal treatment to repair crystal damage. By systematically monitoring various colour centres simultaneously, the team correlated their formation processes and identified nuanced dependencies on process parameters. The work opens exciting possibilities for embedding optically-active artificial atoms directly into silicon, leveraging the compatibility with advanced semiconductor manufacturing.

This breakthrough reveals a suite of SiCC formation processes that can guide the development of future emitter-based devices for scalable quantum photonic technologies. The ability to precisely control the creation of these defects is essential for realising quantum computing and networking applications, including the generation of entangled photons and multi-spin registers. The findings not only advance our understanding of defect formation in silicon but also provide valuable insights for future studies exploring the fundamental mechanisms governing these quantum systems, a crucial step towards realising robust and scalable quantum technologies.

Carbon and Hydrogen Implantation in Silicon-on-Insulator

Scientists investigated the generation of colour centres in silicon-on-insulator (SOI) wafers for scalable quantum photonic technologies. The research team employed commercially available 220nm SOI wafers with a resistivity of ≥3000 Ωcm as their material platform. Carbon and hydrogen ions were implanted using standard recipes with a 1:1 fluence, initially implanting carbon followed by a 1000 ◦C curing anneal for 20 seconds to repair crystal damage, then hydrogen implantation. All reported measurements utilized a 12C implantation fluence of 7 × 1013cm−2, although preliminary data from wafers with a lower 13C fluence of 1 × 1013cm−2 exhibited qualitatively similar results.

Following implantation, the study pioneered a detailed investigation into colour centre activation and nanofabrication processes. Researchers systematically varied low-temperature annealing parameters, exploring temperatures from 200 to 600 ◦C and durations from 30 to 600 seconds. The team also tested additional procedures, including a boiling step in deionised water before activation, process gas flows ranging from 200 to 5000 sccm, and both optical and contact thermal control methods. This comprehensive parameter scan enabled the observation of activation, suppression, and revival mechanisms in colour centre formation as annealing temperatures were altered.

To assess the impact of nanofabrication, the scientists interrupted device fabrication after each targeted step, creating a series of silicon chips for analysis. They specifically examined the effect of oxygen plasma ashing, used for resist removal, over durations from 30 to 600 seconds, comparing it with remote ashing and varying the order of nanofabrication steps. Secondary ion mass spectroscopy (SIMS) measurements were performed on samples implanted with a 5 × 1014cm−2 C12 fluence, both before and after annealing, to map the distribution of implanted carbon and hydrogen ions. The work identified optimised annealing parameters and fabrication procedures, differing from previously reported values, and discerned stable emission lines likely originating from novel colour centres. This suite of optimised processes will guide the development of future silicon-based quantum photonic devices.

Silicon Colour Centre Formation via Thermal Processing

Scientists achieved the generation of several types of colour centres in silicon for mass-manufacturable silicon-on-insulator devices. The research meticulously investigated how thermal and fabrication processes impact the presence of these emitters, revealing coupled formation dynamics between different colour centres. Optimal parameters for processes were identified, alongside a detailed sensitivity analysis regarding duration and nanofabrication procedures for photonic integrated circuits. Furthermore, the study discerned stable optical signals from previously unidentified colour centres in silicon.

Experiments revealed that a 7 × 1013cm−2 carbon implantation fluence, followed by a 20-second 1000 ◦C curing anneal and subsequent hydrogen implantation, yielded optimal results. Detailed secondary ion mass spectroscopy (SIMS) measurements demonstrated a carbon atom distribution centred at a depth of 110nm, while hydrogen distribution peaked at 120nm. The data showed that while thermal annealing did not visibly affect the vertical carbon distribution, hydrogen atoms gradually diffused through the silicon at higher annealing temperatures, consistent with expectations given hydrogen’s small size and high diffusivity. PL signals were consistently observed when the cryostat temperature fell below 40 K, with standard operating temperature maintained at 4.5 K for all reported data. The team identified a range of optically active colour centres, some with unknown atomic structures. Specifically, the W centre, exhibiting an emission energy at 1217.17 ±0.02nm, demonstrated maximum integrated PL intensity at an annealing temperature of 240 ◦C. The G centre, attributed to a tri-interstitial silicon cluster, showed a peak at 1278.6 ±0.05nm with a maximum intensity at 200 ◦C. Measurements confirm that the W, G, C, and M centres were detectable even in the as-implanted sample, prior to activation annealing, indicating their formation is driven by implantation-induced lattice damage.

Silicon Colour Centre Dynamics and CN Identification represent

Scientists have conducted a comprehensive analysis of colour centre formation in silicon, focusing on processes relevant to silicon-on-insulator device fabrication. The research details coupled dynamics between different colour centres during annealing, identifying key parameters for their activation and demonstrating sensitivity to nanofabrication procedures. Specifically, the study establishes an optimal annealing temperature of 525±10°C for activating T centres, a value differing from previous reports. Furthermore, researchers observed stable optical signals originating from previously unidentified colour centres in silicon.

Notably, a clear signal in the S-band was detected, matching the predicted zero-phonon line of the CN colour centre, a recently theorised SiCC with potential for quantum computing and networking. The authors acknowledge that high-intensity plasma cleaning reduces T centre density, but this can be mitigated by adjusting the timing of annealing or employing gentle remote ashing. A limitation noted is the statistical uncertainty represented by error bars in the data. Future work could explore the full potential of the newly identified CN centre and other SiCCs for advanced photonic quantum devices.