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Diamond and Related Materials

Enhancing NV concentration in delta-doped diamond via low-pressure high-temperature annealing

Philip Schätzle, Sven Mägdefessel, Leon Büttner, Patrik Straňák, Aurelién Commans, Lutz Kirste, Rebekka Eberle, V. Cimalla, Peter Knittel

Published Jan 16, 2026• 1 citation
Publisher

Abstract

We present the increase in the nitrogen vacancy center concentration in nitrogen delta-doped layers by almost one order of magnitude. To achieve this, we employ a low-pressure, high-temperature annealing step at 1750 °C in vacuum. We demonstrate an enhancement of the photoluminescence intensity of NV centers compared to annealing steps at lower temperatures of 1200 °C. To achieve this, we fabricate nitrogen-doped thin films with a thickness of 50 nm via chemical vapor deposition. We show that the nitrogen is mainly incorporated in a 6 nm thin film at the layer interface. We link the strong enhancement of the NV concentration to a possible decomposition of NVH centers and the mobility of various species at elevated temperatures, including vacancies and nitrogen in these two-dimensional structures. Additionally, after the high temperature annealing, we observe a Hahn-echo spin coherence time of 7.9 μ s, which is in line with literature data on achievable coherence time in highly nitrogen-doped layers. Our results could pave the way for the precise fabrication of improved diamond elements, e.g., used in magnetic field sensors and offer an alternative route to implantation techniques.

DOI
10.1016/j.diamond.2026.113337

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We present the increase in the nitrogen vacancy center concentration in nitrogen delta-doped layers by almost one order of magnitude. To achieve this, we employ a low-pressure, high-temperature annealing step at 1750 °C in vacuum. We demonstrate an enhancement of the photoluminescence intensity of NV centers compared to annealing steps at lower temperatures of 1200 °C. To achieve this, we fabricate nitrogen-doped thin films with a thickness of 50 nm via chemical vapor deposition. We show that the nitrogen is mainly incorporated in a 6 nm thin film at the layer interface. We link the strong enhancement of the NV concentration to a possible decomposition of NVH centers and the mobility of various species at elevated temperatures, including vacancies and nitrogen in these two-dimensional structures. Additionally, after the high temperature annealing, we observe a Hahn-echo spin coherence time of 7.9 μ s, which is in line with literature data on achievable coherence time in highly nitrogen-doped layers. Our results could pave the way for the precise fabrication of improved diamond elements, e.g., used in magnetic field sensors and offer an alternative route to implantation techniques.
Nitrogen-vacancy (NV) centers in diamonds have been an epicenter of research for diverse applications in quantum technologies. It is therefore imperative that their fabrication techniques are well understood and characterized for the technological scalability of these applications. A comparative study of the optical and spin properties of NVs created by ion implantation and chemical vapor deposition delta-doping is thus presented, combined with an investigation on the impact of annealing in vacuum at different temperatures. In addition, nanopillars are fabricated by electron beam lithography and reactive ion etching for enhanced photon collection efficiency. An extensive combination of characterization techniques is employed. Notably, the smallest nanopillars present fluorescence enhancements of factor around 50, compared to the unstructured regions. Annealing is also demonstrated to increase the optical contrast between the NVs' electronic states, the coherence and relaxation times both in bulk as in pillars. Regarding the NV preparation technique, the delta-doping is shown to create NVs with less lattice defects and strain compared to implantation. • Comparative study of optical and spin properties of implanted and δ-doped CVD NVs • Impact of structuring with nanopillars and annealing on the NV properties • Fluorescence enhancement factors of above 30 in 100–150 nm diameter pillars • 3-Fold increase in ODMR contrast of all samples after annealing • Increase of coherence and relaxation times after annealing
The negatively-charged nitrogen-vacancy (NV) center is the most studied optical center in diamond and is very important for applications in quantum information science. Many proposals for integrating NV centers in quantum and sensing applications rely on their tailored fabrication in ultra pure host material. In this study, we use ion implantation to controllably introduce nitrogen into high purity, low nitrogen chemical vapor deposition diamond samples. The properties of the resulting NV centers are studied as a function of implantation temperature, annealing temperature, and implantation fluence. We compare the implanted NV centers with native NV centers present deep in the bulk of the as-grown samples. The results for implanted NV centers are promising but indicate, at this stage, that the deep native NV centers possess overall superior optical properties. In particular, the implanted NV centers obtained after annealing at 2000 °C under a stabilizing pressure of 8 GPa showed an ensemble linewidth of 0.17 nm compared to 0.61 nm after annealing at 1000 °C. Over the same temperature range, the ensemble NV−/NV0 ratio increased by a factor of ∼5, although this was accompanied by an overall decrease in the NV count.
Nitrogen-vacancy (NV) centers in diamonds have been an epicenter of research for diverse applications in quantum technologies. It is therefore imperative that their fabrication techniques are well understood and characterized for the technological scalability of these applications. A comparative study of the optical and spin properties of NVs created by ion implantation and chemical vapor deposition delta-doping is thus presented, combined with an investigation on the impact of annealing in vacuum at different temperatures. In addition, nanopillars are fabricated with electron beam lithography and reactive ion etching for enhanced photon collection efficiency. An extensive combination of characterization techniques is employed. Notably, the smallest nanopillars present fluorescence enhancements of factor around 50, compared to the unstructured regions. Annealing is also demonstrated to increase the optical contrast between the NVs' electronic states, the coherence and relaxation times both in bulk as in pillars. Regarding the NV preparation technique, the delta-doping is shown to create NVs with less lattice defects and strain compared to implantation.
We demonstrate nanometer-precision depth control of nitrogen-vacancy (NV) center creation near the surface of synthetic diamond using an in situ nitrogen delta-doping technique during plasma-enhanced chemical vapor deposition. Despite their proximity to the surface, doped NV centers with depths (d) ranging from 5 to 100 nm display long spin coherence times, T2 > 100 μs at d = 5 nm and T2 > 600 μs at d ≥ 50 nm. The consistently long spin coherence observed in such shallow NV centers enables applications such as atomic-scale external spin sensing and hybrid quantum architectures.
The sensitivity of magnetic and electric field sensors based on nitrogen-vacancy (NV) center in diamond strongly depends on the available concentration of NV and their coherence properties. Achieving high coherence times simultaneously with high concentration is a challenging experimental task. Here, we demonstrate that by using a temperature gradient method of high-pressure, high-temperature growing technique, one can achieve nearly maximally possible dephasing times, limited only by carbon nuclear spins at low nitrogen concentrations or nitrogen electron spin at high nitrogen concentrations. Hahn-echo T 2 coherence times were also investigated and found to demonstrate reasonable values. Thus, the high-pressure, high-temperature technique is a strong contender to the popular chemical vapor deposition method in the development of high-sensitivity, diamond-based sensors.
Nitrogen-vacancy (NV) centers in diamond photonic nanostructures have attracted much attention as efficient single photon emitters and quantum bits. These quantum optical devices mostly require single or low-density NV centers doped in thin diamond membranes. In contrast, this study focuses on diamond photonic nanostructures with a high concentration of NV centers to achieve a diamond color center laser with a sufficient gain available as a visible light source and a sensitive magnetic-field sensor. We employ high-dose helium ion implantation to type-Ib diamond substrates and thermal annealing, which enables us to obtain uniform thin diamond membranes containing a dense ensemble of NV centers. Luminescence spectroscopy reveals the kinetics of NV centers at high temperature from which we find an optimum annealing temperature maximizing the NV center emission while suppressing the transformation from NV to H3 centers. Furthermore, fine photonic nanowires are also successfully fabricated in the air-suspended diamond membrane, and they exhibit intense photoluminescence from the NV centers with a concentration as high as 7 × 1016 cm−3 (0.4 ppm). These results suggest a route to the fabrication of diamond photonic nanostructures containing a dense ensemble of NV centers, which can be a key material for developing diamond-based light emitting and magnetic-field sensing devices.