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 | Fraunhofer Institute for Applied Solid State Physics, Diamond Materials (Germany) |
| Analysis | Full AI Review Included |
Wafer Scale N-Doped Diamond (111) for Quantum Applications: 6CCVD Technical Analysis
Section titled “Wafer Scale N-Doped Diamond (111) for Quantum Applications: 6CCVD Technical Analysis”This document analyzes the recent research on wafer-scale heteroepitaxial N-doped diamond (111) growth for Nitrogen Vacancy (NV) quantum applications. It highlights the critical material specifications achieved and outlines how 6CCVD’s advanced MPCVD capabilities can meet and exceed the requirements for scalable quantum device fabrication.
Executive Summary
Section titled “Executive Summary”This research successfully demonstrates the feasibility of producing high-quality NV-doped diamond on a wafer scale, achieving performance metrics essential for quantum sensing and computing.
- Wafer-Scale Heteroepitaxy: Successful growth of N-doped diamond on 2” (50 mm) Ir/YSZ/Si (111) substrates using MPCVD and Epitaxial Lateral Overgrowth (ELO).
- Record Coherence Time: Achieved a T₂ coherence time of 9.3 µs, the highest value ever reported for heteroepitaxial diamond (111).
- High T₂/T₂ Ratio:* Demonstrated an exceptional T₂/T₂* ratio of almost 100 (T₂* = 95 ns), indicating that the coherence time is primarily limited by the nitrogen spin bath (P1 centers).
- Preferential Orientation: Observed a strong preferential orientation of NV centers (ca. 90%) along the surface normal, crucial for addressing NVs in quantum devices.
- Layer Structure: The functional material consists of a 50 µm N-Cap layer superimposed on a 23 µm intrinsic diamond layer.
- Material Challenge: The primary limitation identified is heavy strain and fragility in the heteroepitaxial material, which negatively impacts sample stability and T₂* performance.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the research, defining the performance and structural characteristics of the N-doped diamond material.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Wafer Diameter | 50 | mm | Substrate size (2” Ir/YSZ/Si) |
| T₂ Coherence Time (Hahn-Echo) | 9.3 | µs | Highest reported for heteroepitaxial (111) |
| T₂* Dephasing Time (Ramsey) | 95 | ns | Inhomogeneous dephasing time |
| T₂/T₂* Ratio | Almost 100 | - | Indicates spin bath limited coherence |
| N-Cap Layer Thickness | 50 | µm | Nitrogen-doped functional layer |
| Intrinsic Layer Thickness | 23 | µm | Grown via ELO stabilization |
| Total Nitrogen Concentration (P1) | 7.3 | ppm | Measured by ToF-SIMS in N-Cap |
| NV Incorporation Efficiency | 0.1 | % | Ratio of NV centers to total N concentration |
| Preferential NV Orientation | Ca. 90 | % | Along the surface normal |
| Diamond (111) Rocking Curve FWHM | 2.3 | ° | Overall crystal quality |
| N-Cap Growth Frequency | 915 | MHz | Used 915 MHz ellipsoid reactor |
| N-Cap Growth Temperature | 920 | K | CVD process temperature |
| N-Cap Growth Time | 118 | h | Total growth duration for N-Cap |
Key Methodologies
Section titled “Key Methodologies”The heteroepitaxial diamond stack was fabricated using a multi-step MPCVD process involving specialized reactors and techniques to manage strain and promote (111) growth.
- Template Preparation: Ir/YSZ/Si (111) wafers (50.8 mm diameter) were grown using Magnetron Sputtering Epitaxy (MSE).
- Iridium (Ir) Deposition: DC, 70 W power, 975 K temperature, 0.01 Pa pressure.
- Yttria-Stabilized Zirconia (YSZ) Deposition: RF, 250 W power, 1050 K temperature, 0.31 Pa pressure (O₂/Ar ratio 1:2).
- Bias-Enhanced Nucleation (BEN): Diamond was nucleated in a 2.45 GHz ellipsoid reactor with a 370 V bias applied to a ring electrode.
- Recipe: 2.5 kW power, 940 K temperature, 3.5 kPa pressure, CH₄/H₂ ratio 3.2%.
- Epitaxial Lateral Overgrowth (ELO) Structuring: A pixel pattern (5 µm radius, 10 µm pitch) was applied to the nucleated sample to facilitate lateral growth and coalescence.
- Intrinsic Bulk Growth: A 23 µm intrinsic layer was grown in a 2.45 GHz ellipsoid reactor.
- Recipe: 3.8 kW power, 920 K temperature, 6.3 kPa pressure, CH₄/H₂ ratio 1.7%.
- N-Cap Deposition (NV Layer): A 50 µm nitrogen-doped layer was grown in a 915 MHz ellipsoid reactor, optimized for high N incorporation and low twinning.
- Recipe: 11.7 kW power, 920 K temperature, 12 kPa pressure, CH₄/H₂ ratio 0.5%, N₂/H₂ ratio 0.5%.
- Strain Mitigation: Active Si dumping (using randomly oriented diamond pieces) was employed to prevent Si incorporation and subsequent Silicon Vacancy (SiV) center formation.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”The research successfully validated the potential of wafer-scale (111) diamond for quantum applications, but identified significant challenges related to material strain and NV incorporation efficiency. 6CCVD offers specialized MPCVD diamond solutions that directly address these limitations, enabling researchers to move from proof-of-concept to robust, scalable devices.
Applicable Materials
Section titled “Applicable Materials”To replicate the high T₂ performance while mitigating the reported strain and fragility issues, 6CCVD recommends the following materials:
| Material Grade | Application Focus | 6CCVD Advantage |
|---|---|---|
| Optical Grade SCD (111) | Highest T₂ performance, low strain, fundamental research. | Provides the lowest defect density and highest crystalline quality (Ra < 1 nm polished), eliminating the high strain and mosaic tilt observed in heteroepitaxy. Ideal for achieving the theoretical T₂ limit (28 µs). |
| High-Purity PCD (111) | Wafer-scale HVM, cost-sensitive applications. | Available in large formats (up to 125 mm diameter) with controlled (111) orientation, offering a scalable alternative to the 2” heteroepitaxial approach. |
| Custom N-Doped SCD/PCD | Optimized NV density and depth profiling. | We offer precise control over nitrogen flow and growth parameters to maximize NV incorporation efficiency (targeting > 0.25%) and achieve 100% preferential orientation. |
Customization Potential
Section titled “Customization Potential”6CCVD’s in-house engineering and fabrication services are designed to meet the precise, complex requirements of quantum device integration:
- Wafer Scale & Dimensions: While the paper demonstrated 50 mm (2”) heteroepitaxy, 6CCVD provides Polycrystalline Diamond (PCD) plates up to 125 mm in diameter, enabling true high-volume manufacturing scale-up.
- Precision Thickness: We offer SCD and PCD layers with thickness control from 0.1 µm up to 500 µm, allowing researchers to precisely tailor the 50 µm N-Cap layer depth or create complex multi-layer structures.
- Advanced Polishing: We guarantee ultra-smooth surfaces, critical for subsequent lithography and device integration. Our polishing achieves Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD.
- Custom Metalization: For integrating NV centers into functional quantum devices (e.g., microwave delivery structures, electrodes), 6CCVD offers internal metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu deposition.
Engineering Support
Section titled “Engineering Support”The primary challenge identified in this research—heavy strain leading to sample fragility and T₂* degradation—is inherent to heteroepitaxial growth. 6CCVD’s in-house PhD team specializes in mitigating these issues through optimized homoepitaxial growth recipes.
- Strain Mitigation: Our experts can assist with material selection for similar NV Quantum Sensing projects, recommending low-strain SCD (111) substrates to achieve superior T₂* and T₂ performance, surpassing the limits imposed by the heteroepitaxial template.
- Recipe Optimization: We provide consultation on achieving maximum NV orientation purity and optimizing the N-doping profile to push the T₂ coherence time closer to the theoretical P1 limit of 28 µs.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
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 .