Wafer Scale N‐Doped Diamond (111) with Mainly Nitrogen Spin Bath Limited Nitrogen Vacancy Coherence Times from Heteroepitexial Growth
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-10-08 |
| Journal | physica status solidi (RRL) - Rapid Research Letters |
| Authors | Jürgen Weippert, Jan Engels, Jan Kustermann, T. Fehrenbach, C. Wild |
| Institutions | Diamond Materials (Germany), Fraunhofer Institute for Applied Solid State Physics |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research details the successful wafer-scale heteroepitaxial growth of N-doped Diamond (111) on Ir/YSZ/Si templates, achieving performance metrics critical for quantum technology applications.
- Record Coherence Time: A T2 coherence time of 9.3 µs was achieved in the N-Cap layer, the highest value ever reported for heteroepitaxial diamond (111).
- Spin Bath Limitation: The material exhibits an exceptionally high T2/T2* ratio of approximately 100 (T2* = 95 ns), suggesting the coherence time is primarily limited by the nitrogen spin bath (P1 centers).
- Preferential Orientation: Strong preferential orientation of the negatively charged Nitrogen Vacancy (NV-) centers was confirmed, with 90% aligned perpendicular to the (111) surface.
- Wafer-Scale Platform: The growth was demonstrated on 2” Ir/YSZ/Si (111) wafers, utilizing Bias-Enhanced Nucleation (BEN) and Epitaxial Lateral Overgrowth (ELO) for morphology control.
- Doping Efficiency: The N-Cap layer has a total nitrogen concentration of 7.3 ppm (1.3 x 1018 cm-3), resulting in an NV incorporation efficiency of 0.1%.
- Primary Challenge: Significant material strain and fragility remain the major challenge, requiring further optimization to ensure sample stability and maximize quantum performance.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Wafer Diameter | 50 | mm | Ir/YSZ/Si (111) Substrate |
| Diamond Orientation | (111) | Crystal Plane | Heteroepitaxial Growth |
| T2 Coherence Time | 9.3 | µs | Hahn-Echo, N-Cap layer |
| T2* Dephasing Time | 95 | ns | Ramsey Experiment, N-Cap layer |
| T2/T2* Ratio | ~100 | Dimensionless | High ratio, indicating spin bath limitation |
| Total N Concentration | 7.3 | ppm | ToF-SIMS, N-Cap (1.3 x 1018 cm-3) |
| NV Incorporation Efficiency | 0.1 | % | Relative to total substitutional N |
| Preferential NV Orientation | 90 | % | Along surface normal (cw-ODMR) |
| N-Cap Thickness | 50 | µm | Final doped layer |
| Intrinsic Layer Thickness | 23 | µm | Bulk growth layer |
| Diamond 111 FWHM (Rocking Curve) | 2.3 | ° | Overall crystal quality |
| Diamond 220 FWHM (Omega Scan) | ~4 | ° | Related to mosaic tilt and twist |
| NV0/NV- Charge State Ratio | 7 - 8 | % | Calculated from PL spectra |
Key Methodologies
Section titled “Key Methodologies”The diamond film was grown using a multi-step Plasma-Enhanced Chemical Vapor Deposition (PECVD) process on a sputtered Ir/YSZ/Si (111) template.
- Substrate Preparation: Iridium (Ir) and Yttria-Stabilized Zirconia (YSZ) buffer layers were deposited epitaxially on 50.8 mm Si (111) substrates via Magnetron Sputtering Epitaxy (MSE).
- Nucleation: Diamond was nucleated using Bias-Enhanced Nucleation (BEN) in a 2.45 GHz ellipsoid reactor (370 V bias applied).
- Morphology Control: Epitaxial Lateral Overgrowth (ELO) structuring was performed using a pixel pattern (5 µm radius, 10 µm pitch) to promote lateral growth and coalescence.
- Intrinsic Bulk Growth: A 23 µm intrinsic layer was grown in a 2.45 GHz ellipsoid reactor (920 K, 6.3 kPa, 1.7% CH4/H2).
- N-Cap Deposition: The final 50 µm nitrogen-doped layer (N-Cap) was deposited using a 915 MHz ellipsoid reactor (11.7 kW power, 920 K, 12 kPa). This frequency was chosen for higher nitrogen doping efficiency and reduced twinning.
- Impurity Management: Active Silicon (Si) dumping was implemented during N-Cap growth (using randomly oriented diamond pieces) to prevent Si incorporation and subsequent formation of Silicon Vacancy (SiV) centers.
- Spectroscopic Analysis:
- T2 coherence time was determined using the Hahn-Echo optically detected magnetic resonance (ODMR) pulse sequence.
- T2* dephasing time was determined using the Ramsey pulse sequence.
- Nitrogen concentration was measured via Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS).
Commercial Applications
Section titled “Commercial Applications”The development of wafer-scale, highly oriented, high-coherence NV-doped diamond (111) directly addresses the manufacturing requirements for next-generation quantum technologies.
- Quantum Sensing: Enables the mass production of high-sensitivity magnetic field sensors, gyroscopes, and thermometers based on NV center spin properties, particularly for medical imaging (MRI) or navigation systems.
- Integrated Quantum Devices: The preferential 90% NV orientation along the surface normal is essential for coupling NV centers to integrated photonic structures (waveguides, resonators) on a chip, facilitating scalable quantum networks and processors.
- Room Temperature Quantum Computing: Provides a pathway for fabricating diamond-based quantum registers and memory elements that operate reliably at room temperature, leveraging the long T2 coherence time.
- Wafer-Scale Manufacturing: The successful growth on 2” Si-based templates moves diamond quantum material fabrication toward standard semiconductor processing scales, reducing cost and increasing throughput.
- Advanced Material Research: Serves as a foundational platform for further heteroepitaxial optimization, focusing on strain reduction and defect engineering to push T2 times closer to the theoretical P1 limit (28 µs).
View Original 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 .