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physica status solidi (RRL) - Rapid Research Letters

Wafer Scale N‐Doped Diamond (111) with Mainly Nitrogen Spin Bath Limited Nitrogen Vacancy Coherence Times from Heteroepitexial Growth

Jürgen Weippert, Jan Engels, Jan Kustermann, T. Fehrenbach, Christoph Wild, Patricia Klar, Patrik Straňák, Mario Prescher, Lutz Kirste, Sven Mägdefessel, Peter Knittel, V. Lebedev

Published Oct 8, 2025• 2 citations
Publisher

Abstract

Diamond (111) is grown heteroepitaxially on 2″ Ir/YSZ/Si (111) wafers (YSZ=yttria‐stabilized zirconia) with a diameter of 50 mm and off‐cuts of up to 6, applying plasma‐enhanced chemical vapor deposition supported by bias‐enhanced nucleation and epitaxial lateral overgrowth. In the final growth step, a nitrogen‐doped layer (N‐Cap) is superimposed. In the N‐Cap, a preferential orientation of nitrogen vacancy (NV) centers along the surface normal is observed, which has a T coherence time of 9.3 μs, which is the highest value ever reported for heteroepitaxial diamond (111). In the meantime, the T dephasing time is 95 ns, which means that the T / T ratio is almost 100, while published ratios for homoepitaxial diamond are in the range 5–20. The total nitrogen concentration as measured by Time‐of‐Flight Secondary Ion Mass Spectrometry is determined to be 7.3 ppm, which, in combination with photoluminescence analysis, yields an NV incorporation efficiency of .

DOI
10.1002/pssr.202500171

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Diamond (111) is grown heteroepitaxially on 2″ Ir/YSZ/Si (111) wafers (YSZ=yttria‐stabilized zirconia) with a diameter of 50 mm and off‐cuts of up to 6, applying plasma‐enhanced chemical vapor deposition supported by bias‐enhanced nucleation and epitaxial lateral overgrowth. In the final growth step, a nitrogen‐doped layer (N‐Cap) is superimposed. In the N‐Cap, a preferential orientation of nitrogen vacancy (NV) centers along the surface normal is observed, which has a T coherence time of 9.3 μs, which is the highest value ever reported for heteroepitaxial diamond (111). In the meantime, the T dephasing time is 95 ns, which means that the T / T ratio is almost 100, while published ratios for homoepitaxial diamond are in the range 5–20. The total nitrogen concentration as measured by Time‐of‐Flight Secondary Ion Mass Spectrometry is determined to be 7.3 ppm, which, in combination with photoluminescence analysis, yields an NV incorporation efficiency of .
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Abstract A platform for heteroepitaxial (111) chemical vapor deposition (CVD) diamond quantum sensors with preferentially aligned nitrogen vacancy (NV) centers on a large substrate is developed, and its operation as an electric vehicle (EV) battery monitor is demonstrated. A self‐standing heteroepitaxial CVD diamond film with a (111) orientation and a thickness of 150 µm is grown on a non‐diamond substrate and subsequently separated from it. The high uniformity and crystallinity of the (111)‐oriented diamond is confirmed. A 150‐µm thick NV‐diamond layer is then deposited on the heteroepitaxial diamond. The T 2 value measured by confocal microscopy is 20 µs, which corresponds to substitutional nitrogen defect concentration of 8 ppm. The nitrogen‐vacancy concentration and T 2 * are estimated to be 0.05 ppm and 0.05 µs by continuous wave optically detected magnetic resonance (CW‐ODMR) spectroscopy in a fiber‐top sensor configuration. In a gradiometer, where two sensors are placed on both sides of the busbar, the noise floor is 17 nT/Hz 0.5 in the frequency range of 10–40 Hz without magnetic shielding. The Allan deviation of the magnetic field noise in the laboratory is below 0.3 µT, which corresponds to a busbar current of 10 mA, in the accumulation time range of 10 ms to 100 s.
Heteroepitaxial chemical vapor deposition is the most promising option to fabricate wafer-scale monocrystalline diamonds for quantum applications. Previously, we demonstrated the feasibility to manufacture functional micrometer-sized pyramids on as-grown heteroepitaxial diamond as well as their quantum optical characteristics. Due to high background signals and microfabrication challenges, these pyramids could not compete with homoepitaxially grown structures. In this study, we overcame these problems with a nominally undoped buffer layer between the heteroepitaxial substrate and the pyramidal microstructure to reduce the signal-to-noise ratio from the substrate on the spin measurements of the nitrogen-vacancy (NV) center. Moreover, the microfabrication was improved to reach a higher angle of the pyramidal side plane, corresponding to the {111} facets. These improvements lead to pyramids on which each facet contains almost purely only one of the four possible NV orientations as shown by optically detected magnetic resonance (ODMR). ODMR shows a very high contrast of 19% without an external magnet and of 13% for a single spin resonance in the presence of a magnetic field. The contrast is more than doubled compared to our previous study. The T2* dephasing time of the NV centers of the samples ranges from 0.02 to 0.16 μs. The P1 center is a single substitutional nitrogen center, and the P1 densities range from 1.8 to 5 ppm.
We investigate native nitrogen vacancy (NV) and silicon vacancy (SiV) color centers in a commercially available, heteroepitaxial, wafer-sized, mm thick, single-crystal diamond. We observe single, native NV centers with a density of roughly 1 NV per μm3 and moderate coherence time (T2 = 5 μs) embedded in an ensemble of SiV centers. Using low temperature luminescence of SiV centers as a probe, we prove the high crystalline quality of the diamond especially close to the growth surface, consistent with a reduced dislocation density. Using ion implantation and plasma etching, we verify the possibility to fabricate nanostructures with shallow color centers rendering our material promising for fabrication of nanoscale sensing devices. As this diamond is available in wafer-sizes up to 100 mm, it offers the opportunity to up-scale diamond-based device fabrication.
Here, we report the fabrication and characterization of single crystal diamond films on a two-inch wafer-scale containing three-dimensional layered structures of negatively charged nitrogen-vacancy color centers (NV−^{-}−). The (100)-oriented layered diamond films were grown by chemical vapor deposition (CVD) to create spatially separated regions of enhanced emission associated with NV−^{-}− centers. Such localized emission enhancement as well as 2D and 3D arrays of spins could enable close-packed architectures for emerging quantum devices, such as data processors, memory cells, and magnetic sensors. A cyclic sequence of CVD growth and oxygen-plasma etching is employed, resulting in the in-situ formation of layered inverted pyramidal structures with flat $\{111111111\}$ sidewalls. These pits are subsequently overgrown by nitrogen-doped diamond to achieve NV−^{-}−-rich facets with a uniform N-V bond arrangement and improved nitrogen incorporation efficiency.
Abstract The nitrogen-vacancy (NV) center in diamond is a promising quantum system for magnetometry applications exhibiting optical readout of minute energy shifts in its spin sub-levels. Key material requirements for NV ensembles are a high NV − concentration, a long spin coherence time and a stable charge state. However, these are interdependent and can be difficult to optimize during diamond growth and subsequent NV creation. In this work, we systematically investigate the NV center formation and properties in bulk chemical vapor deposition (CVD) diamond. The nitrogen flow during growth is varied by over four orders of magnitude, resulting in a broad range of single substitutional nitrogen concentrations of 0.2–20 parts per million. For a fixed nitrogen concentration, we optimize electron-irradiation fluences with two different accelerated electron energies, and we study defect formation via optical characterizations. We discuss a general approach to determine the optimal irradiation conditions, for which an enhanced NV concentration and an optimum of NV charge states can both be satisfied. We achieve spin–spin coherence times T 2 ranging from 45.5 to 549 μ s for CVD diamonds containing 168 to 1 parts per billion NV − centers, respectively. This study shows a pathway to engineer properties of NV-doped CVD diamonds for improved sensitivity.