⚛️ quantum physics

Efficient formation and identification of single emitters in 4H-SiC following maskless heavy ion implantation

This paper demonstrates an efficient method for creating and rapidly identifying bright single-photon emitters in 4H-SiC using maskless heavy-ion implantation of bismuth and tin, combined with a tiered characterization scheme that eliminates the need for time-consuming low-temperature spectroscopy.

Original authors: S. Eserin, L. K. S. Zimmermann, E. Schneider, M. Ludlow, J. Heiler, O. G. Lloyd-Willard, K. Stockbridge, G. Aresta, L. Antwis, S. K. Clowes, M. Hofmann, S. Kucera, P. Berwian, F. Kaiser, B. N. Murdin

Published 2026-08-28

📖 4 min read🧠 Deep dive

CC BY 4.0

Original authors: S. Eserin, L. K. S. Zimmermann, E. Schneider, M. Ludlow, J. Heiler, O. G. Lloyd-Willard, K. Stockbridge, G. Aresta, L. Antwis, S. K. Clowes, M. Hofmann, S. Kucera, P. Berwian, F. Kaiser, B. N. Murdin

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

In the quest to build quantum computers and ultra-sensitive sensors, scientists are searching for tiny, reliable sources of single particles of light. These sources, known as single-photon emitters, act as the fundamental bits of information for future technologies. One of the most promising materials for hosting these sources is silicon carbide, a hard, durable crystal often used in industrial cutting tools but now prized for its ability to trap specific defects that glow with quantum properties. Among these defects, a particular type involving an oxygen-vacancy complex has shown exceptional brightness and the ability to be read out using simple magnetic techniques, even at room temperature. However, creating these specific defects exactly where they are needed, and then quickly finding the good ones among the bad, has remained a difficult and slow process, often requiring complex machinery and freezing temperatures.

A team of researchers has now demonstrated a faster, more direct way to create and identify these useful light sources. By using a focused beam of heavy metal ions, specifically bismuth and tin, they created precise damage sites within a sheet of silicon carbide without using any physical masks to guide the beam. This "maskless" approach allowed them to place these ion impacts in a grid pattern with high accuracy. After the ions struck the material, creating dense collision cascades of vacancies, the researchers heated the samples to temperatures between 900 and 1000 degrees Celsius. This heat healed the damage caused by the ions and encouraged the atoms to rearrange, forming the desired glowing defects. The process proved highly effective: in the best conditions, up to 18 percent of the spots where ions were fired ended up hosting a single, bright emitter.

Once the emitters were formed, the challenge shifted to finding the right ones quickly. The team developed a step-by-step screening method that avoids the need for time-consuming, low-temperature measurements that usually require expensive cooling equipment. They first looked for spots that were bright enough to be useful, filtering out the dimmer, less promising locations. Next, they measured how the light from these spots responded to different polarizations and how quickly the brightness saturated under strong laser light. By comparing these simple, room-temperature measurements against the specific magnetic resonance frequencies of the emitters, they could reliably distinguish between different types of defects. This tiered approach allowed them to identify the most valuable emitters without ever needing to cool the sample down to near absolute zero.

The study also provided a clear picture of how many ions are needed to get the best results. The researchers found that firing too few ions often failed to create a defect, while firing too many tended to create clusters of multiple defects in the same spot, which are less useful for quantum applications. They calculated that there is a specific "sweet spot" in the number of ions per location that maximizes the chance of getting exactly one emitter. For the bismuth ions used, this optimal number was around 620 ions per spot, while for tin, it was roughly 1100 ions. At these doses, the difference between getting a single useful emitter and getting a messy cluster is at its greatest.

The researchers confirmed that the specific type of emitter they were looking for, known as the PL6 center, consistently showed up with a unique combination of brightness, magnetic response, and lack of polarization dependence. They observed that while the magnetic resonance frequency of these emitters varied slightly from spot to spot, likely due to tiny strains left over from the ion impacts, the overall pattern remained distinct enough to identify them with confidence. This work suggests that heavy-ion implantation is a viable and efficient route for manufacturing large arrays of single-photon emitters. By combining this precise creation method with a rapid, room-temperature screening process, the path opens up for producing the vast numbers of reliable quantum sources needed to build scalable quantum devices.

Technical Summary: Efficient Formation and Identification of Single Emitters in 4H-SiC Following Maskless Heavy Ion Implantation

Problem Statement
Silicon carbide (SiC) is a leading platform for scalable quantum technologies due to its compatibility with industrial wafer-scale processing and the presence of various quantum emitters. While oxygen-vacancy-related emitters (specifically the PL5–8 family, reassigned as OCVSi complexes) offer high optical brightness and strong spin readout contrast, a significant barrier to their utilization in scalable devices is the challenge of maskless formation and rapid identification. Existing methods often rely on ensemble measurements or require time-consuming cryogenic spectroscopy for emitter classification. Furthermore, the systematic exploration of maskless, focused heavy-ion implantation for generating isolated single emitters in 4H-SiC has been limited.

Methodology
The authors fabricated single emitters in 4H-SiC using a maskless Focused Ion Beam (FIB) system (Ionoptika QOne) equipped with a liquid metal alloy ion source.

Implantation: Arrays of 10 × 10 spots were created using heavy ions of Bismuth (Bi) and Tin (Sn) in singly and doubly charged states (Bi+/2+, Sn+/2+). The implantation was performed at a fixed anode voltage of 25 kV (resulting in 25 keV for singly charged and 50 keV for doubly charged ions). Doses ranged from 10 to 200 ions per spot.
Annealing: Nine samples were processed; eight were annealed in an argon atmosphere at temperatures between 600°C and 1100°C, while one remained unannealed as a reference.
Characterization: A tiered characterization scheme was employed:
1. Confocal Photoluminescence (PL) Mapping: Performed at room temperature using 940 nm off-resonant excitation to suppress competing VSi emission. An intensity threshold (>40 kcts/s) was applied to filter out residual damage and identify bright candidates.
2. Photon Correlation: Second-order autocorrelation measurements ( $g^{(2)}(\tau)$ ) using a Hanbury-Brown-Twiss setup confirmed single-photon emission ( $g^{(2)}(0) < 0.5$ ).
3. Emitter Classification: A combination of Optically Detected Magnetic Resonance (ODMR) at zero magnetic field, Polarisation (POL) dependence, Saturation Count Rate (SAT), and Low-Temperature Photoluminescence (LTPL) at 4 K was used to assign emitter types (PL4, PL5, PL6).

Key Contributions and Results

Formation Efficiency: The study demonstrated that up to 18% of implanted sites host a single emitter under optimal conditions. The optimal annealing window was identified as 900–1000°C. Below 900°C, vacancies lack mobility to form stable complexes; above 1100°C, emitters are lost due to annihilation or aggregation.
Dose Optimization: Using a Poissonian model, the authors estimated the optimal implantation dose to maximize single-emitter yield while minimizing multi-emitter sites. For Bi2+, the peak single-emitter fraction occurs at ~1235 ions/spot, while the optimal dose for maximizing the difference between single and multiple emitter probabilities is ~620 ions/spot.
Spatial Accuracy: The implantation accuracy was determined to have a Root Mean Square (RMS) displacement of 146 nm for Bi2+ spots, significantly larger than the ion straggle (3.7 nm), suggesting beam scanning errors or broad beam tails are the dominant factors.
Rapid Identification Scheme: The authors established a correlation-based classification method that avoids the need for cryogenic systems for PL6 identification.
- PL6 vs. PL5: PL6 centres consistently show no polarisation dependence (Degree of Polarisation, DOP $\approx$ 0) and high saturation count rates (>75 kcps), whereas PL5 centres show polarisation dependence.
- ODMR Signatures: PL6 centres exhibit a single ODMR dip, while PL5 centres show two dips.
- PL4 Identification: Identification of PL4 centres still requires LTPL to detect Zero-Phonon Lines (ZPL) at ~1078 nm, as room-temperature ODMR contrast is low.
Yield Statistics: In the Bi2+ 200 ions/spot array annealed at 900°C, 5 of 18 confirmed single emitters were identified as PL6, and 2 as PL5. In the corresponding Sn2+ array, 1 of 6 was PL6. The single-emitter yield per ion was calculated at 0.09% for Bi2+ and 0.05% for Sn2+.

Significance and Claims
The paper claims to establish maskless heavy-ion implantation as an efficient route for forming positioned single emitters in silicon carbide. By combining heavy-ion implantation with a tiered screening process, the authors demonstrate a pathway to rapidly identify promising emitters (specifically PL6) without the necessity of time-consuming low-temperature spectroscopy. The work suggests that while current yields are modest, the ability to screen candidates based on room-temperature metrics (intensity, polarisation, saturation, and ODMR) offers a scalable strategy for future quantum sensing and device integration. The authors note that the formation of oxygen-vacancy complexes (PL5/6) in the absence of implanted oxygen is attributed to residual lattice or surface-bound oxygen, and suggest that future work using oxygen-containing gas species could further improve generation yields.

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