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arXiv:2605.24157

Impact of Surface Treatment on Noise in PL-Measurements of Silicon Vacancies in 4H-SiC Lateral pin-Diodes

Jannik H. Schwarberg, Fabian Magerl, Susanne Beuer, Alexander May, Christian Gobert, Martin Siebert, Christian Miersch, Heino Möller, Wolfgang Knolle, Chihang Luo, Jan F. Dick, Franziska C. Beyer, Mathias Rommel, Jörg Schulze

quant-phSubmitted May 22, 2026• Announced May 26, 2026
arXivHTMLPDF

Abstract

Silicon vacancies ($V_\mathrm{Si}$) in 4H-SiC are promising candidates for quantum technologies due to their long spin coherence times and integrability into mature semiconductor platforms. However, conventional CMOS-compatible processing introduces significant photoluminescence noise from passivation layers and crystal damage, degrading color center coherence and excitation linewidths. This work evaluates strategies to minimize such background noise. Thermally grown oxides with nitrogen monoxide annealing provide excellent low-noise passivation, remaining stable during subsequent $600\,^{\circ}\mathrm{C}$ thermal treatments. Furthermore, combining reactive ion etching with atomic layer etching eliminates ion-induced surface damage. Into lateral pin-diodes, used for stark shift and photoluminescent excitation linewidth tuning, a selectively etched optical window is integrated. These devices show ideal electrical properties -- blocking up to $150\,\mathrm{V}$ with leakage current below $10\,\mathrm{pA}/μ\mathrm{m}$ -- while significantly enhancing the $V_\mathrm{Si}$ environment. Single emitters in these pin-diodes show an increased signal-to-noise ratio of 15 for near-surface and of 50 for deeper emitters on both c-plane and a-plane wafers.

DOI
10.1021/acs.nanolett.6c00646
Comments
38 pages (main text and SI), 8 figures, published in Nano Letters

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Silicon vacancies (VSiV_\mathrm{Si}VSi​) in 4H-SiC are promising candidates for quantum technologies due to their long spin coherence times and integrability into mature semiconductor platforms. However, conventional CMOS-compatible processing introduces significant photoluminescence noise from passivation layers and crystal damage, degrading color center coherence and excitation linewidths. This work evaluates strategies to minimize such background noise. Thermally grown oxides with nitrogen monoxide annealing provide excellent low-noise passivation, remaining stable during subsequent 600 ∘C600\,^{\circ}\mathrm{C}600∘C thermal treatments. Furthermore, combining reactive ion etching with atomic layer etching eliminates ion-induced surface damage. Into lateral pin-diodes, used for stark shift and photoluminescent excitation linewidth tuning, a selectively etched optical window is integrated. These devices show ideal electrical properties -- blocking up to 150 V150\,\mathrm{V}150V with leakage current below 10 pA/μm10\,\mathrm{pA}/μ\mathrm{m}10pA/μm -- while significantly enhancing the VSiV_\mathrm{Si}VSi​ environment. Single emitters in these pin-diodes show an increased signal-to-noise ratio of 15 for near-surface and of 50 for deeper emitters on both c-plane and a-plane wafers.
Silicon T centers are promising spin-photon interfaces in solid-state platforms for telecom-compatible, scalable quantum information technologies. A major challenge for T centers in nanophotonics is spectral diffusion, where fluctuations in the local electric-field environment from surface and bulk charge states broaden the optical transition and reduce photon indistinguishability. Strategies that directly suppress spectral diffusion are therefore critical for improving T-center-based quantum photonic devices. Here, we use atomic-layer-deposited Al2O3 to passivate the silicon surface and demonstrate a systematic narrowing of T center optical linewidths. Across our measurements, Al2O3 passivation reduces the T center emission linewidth by up to 57%. Complementary above-bandgap illumination and spectral hole burning measurements show that the remaining linewidth contains a significant spectral-diffusion component caused by adjacent charge traps, while placing an upper bound of approximately 75 MHz on the homogeneous linewidth. This work provides a CMOS-compatible path toward generating indistinguishable photons from silicon T centers for scalable quantum photonic applications.
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Solid-state spin defects hold great promise as building blocks for various quantum technologies. Embedding spin centers in ppp-nnn diodes under reverse bias has proved to be a powerful strategy to narrow the optical linewidth and increase spin coherence, while also enabling control of the photoluminescence wavelength via Stark shift. Given the multitude of parameters influencing spin centers in diodes (e.g., doping densities and profiles, temperature, bias voltage, spin center position), a question that has not yet been answered is: which set of these design parameters maximizes spin center coherence? In this work, we address this question by developing a scaled gradient descent optimization algorithm that minimizes the optical linewidth of spin centers by combining the numerical solution of a diode's Poisson equation with calculated charge noise from the non-depleted regions. Our optimization is performed for both single- and multiple-parameter cases for divacancies in SiC ppp-iii-nnn diodes, including reverse-bias voltage, doping density and profile, and diode total length. Importantly, the optimization is subject to realistic physical constraints, such as small operating bias voltages, avoidance of the dielectric breakdown regime and physical thresholds for doping density. Additionally, due to the leakage current at reverse bias voltages, we develop a new formalism to investigate its influence on coherence. We show that the corresponding noise can be mitigated by implanting spin defects away from the diode's surfaces. Our work provides guidance on experimentally relevant diodes for hosting spin centers with the narrowest optical linewidths and longest coherence times.
Single photon emitters in silicon carbide (SiC) are a leading platform for scalable quantum technologies. Recent interest has focused on oxygen-vacancy-related emitters, which show exceptionally high optical brightness and strong spin readout contrast. One barrier to scalable quantum devices based on these emitters is the challenge of maskless formation and rapid identification. Here, we demonstrate the formation of isolated bright single emitters in 4H-SiC, using low-energy maskless implantation of heavy ions bismuth and tin. Following annealing, up to 18% of implanted sites host a single emitter, with optimal yields achieved at annealing temperatures of 900-1000 degrees C. Occupancy statistics are modelled to estimate the implantation dose that maximises single-emitter yield. We introduce a tiered characterisation scheme, where a simple intensity threshold isolates single-emitter candidates, confirmed through photon correlation measurements, after which correlations between polarisation, saturation count rate and magnetic resonance frequency assign emitter type. It is shown that time-consuming low-temperature spectroscopy is not necessary to distinguish emitter types. Together, maskless heavy-ion implantation and selective screening offer an efficient route to forming and rapidly identifying near-surface single emitters for room-temperature quantum technologies such as quantum sensing.
The unrivaled maturity of its nanofabrication makes silicon a promising hardware platform for quantum information processing. To this end, efficient single-photon sources and spin-photon interfaces have been implemented by integrating color centers or erbium dopants into nanophotonic resonators. However, the optical emission frequencies in this approach are subject to temporal fluctuations on both long and short timescales, which hinders the development of quantum applications. Here, we investigate this limitation and demonstrate that it can be alleviated by integrating the emitters into Fabry-Perot instead of nanophotonic resonators. Their larger optical mode volume enables both increasing the distance to crystal surfaces and operating at a lower dopant concentration, which reduces implantation-induced crystal damage and interactions between emitters. As a result, we observe a fivefold reduction of the spectral diffusion linewidth down to 4.0(2) MHz. Calculations and experimental investigations of isotopically purified 28-Si crystals suggest that the remaining spectral instability is caused by laser-induced electric-field fluctuations. In direct comparison with a nanophotonic device, the instability is significantly reduced at the same intracavity power, enabling a tenfold increase of the optical coherence time up to 20(1) microseconds. These findings represent a key step towards spectrally stable spin-photon interfaces in silicon and their potential applications in quantum networking and distributed quantum information processing.
Scalable realizations of quantum network technologies utilizing the nitrogen-vacancy (NV) center in diamond require creation of optically coherent NV centers in close proximity to a surface for coupling to optical structures. We create single NV centers by 15N^{15}\mathrm{N}15N ion implantation and high-temperature vacuum annealing. The origin of the NV centers is established by optically detected magnetic resonance spectroscopy for nitrogen isotope identification. Near-lifetime-limited optical linewidths (<60MHz)(<60 \mathrm{MHz})(<60MHz) are observed for the majority of the normal-implant (${7}^{\ensuremath{\circ}}$, $\ensuremath{\approx}100$ nm deep) 15NV^{15}\mathrm{NV}15NV centers. Long-term stability of the ${\mathrm{NV}}^{\ensuremath{-}}$ charge state and emission frequency is demonstrated. The effect of NV-surface interaction is investigated by varying the implantation angle for a fixed ion energy, and thus lattice damage profile. In contrast to the normal-implant condition, NVs from an oblique implant (${85}^{\ensuremath{\circ}}$, $\ensuremath{\approx}20$ nm deep) exhibit substantially reduced optical coherence. Our results imply that the surface is a larger source of perturbation than implantation damage for shallow implanted NVs. This work supports the viability of ion implantation for formation of optically stable NV centers. However, careful surface preparation will be necessary for scalable defect engineering.