FEATURES OF THE TECHNOLOGY OF HOMOEPITAXIAL CHEMICAL DEPOSITION OF THIN DIAMOND LAYERS ON A NITROGEN-DOPED SINGLE-CRYSTAL DIAMOND SUBSTRATE
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-06-20 |
| Journal | IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENIY KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA |
| Authors | С. А. Тарелкин, Н. В. Корнилов, М. С. Кузнецов, Nikolay V. Luparev, S. Yu. Martyushov |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Nitrogen-Doped SCD for Betavoltaic Converters
Section titled “Technical Documentation & Analysis: Nitrogen-Doped SCD for Betavoltaic Converters”Executive Summary
Section titled “Executive Summary”This research demonstrates the critical dependence of diamond betavoltaic converter performance on the crystalline quality and nitrogen (N) doping level of the single-crystal diamond (SCD) substrate. The findings underscore the necessity of ultra-low defect materials, a core strength of 6CCVD’s MPCVD capabilities.
| Feature | Summary | Core Value Proposition |
|---|---|---|
| Application | High-temperature, durable radioisotope energy converters (Betavoltaics) using 63Ni. | Enables long-life power sources for extreme environments (up to 500 °C). |
| Key Finding | High N concentration (300 ppm) in HPHT substrates leads to high structural defects (106-107 cm-2) and high leakage current, rendering devices ineffective. | 6CCVD Solution: Our MPCVD SCD offers superior crystalline quality and precise doping control, minimizing inherited defects. |
| Optimal Performance | Achieved using low N concentration (60 ppm) substrates, resulting in low leakage current and efficient conversion. | Confirms the need for low-defect SCD (Dislocation density: 103-105 cm-2). |
| Performance Metrics | Maximum electrical power of 170 pW with approximately 1% efficiency, operating up to 500 °C. | Demonstrates diamond’s potential for high-temperature, radiation-hardened electronics. |
| Device Structure | n-type Schottky diodes (Pt/i-layer/n+ substrate) fabricated using homoepitaxial CVD growth. | Requires precise control over thin-film deposition and custom metalization, both offered by 6CCVD. |
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the study, highlighting the material requirements and achieved device performance.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optimal N Concentration | 60 | ppm | HPHT Substrate (low leakage) |
| High N Concentration | 300 | ppm | HPHT Substrate (high leakage) |
| Optimal Dislocation Density | 103-105 | cm-2 | Required for efficient conversion |
| High Defect Dislocation Density | 106-107 | cm-2 | Leads to high leakage current |
| Maximum Operating Temperature | 500 | °C | Betavoltaic operation |
| Maximum Electrical Power | 170 | pW | Achieved with 60 ppm N substrate |
| Conversion Efficiency (Max) | ~1 | % | Achieved with 60 ppm N substrate |
| Homoepitaxial Layer Thickness | 30 | µm | Target thickness (i-layer) |
| Schottky Contact Thickness | < 20 | nm | Platinum (Pt) |
| Ohmic Contact Annealing Temp | 700 | °C | Ti/Pt contact formation |
Key Methodologies
Section titled “Key Methodologies”The experiment involved a two-step material synthesis process followed by device fabrication and testing.
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Substrate Preparation (TG-HPHT Growth):
- Method: Temperature Gradient High-Pressure High-Temperature (TG-HPHT) synthesis.
- Doping: Nitrogen (N) was incorporated using atmospheric nitrogen getter (Al) in the Fe-Co-C growth system.
- Doping Levels: Two types of n+ substrates were produced: 300 ppm (~5×1019 cm-3) and 60 ppm (~1019 cm-3).
- Substrate Dimensions: Rectangular plates, 3.5×3.5 mm2, 250 µm thick, (001) orientation.
- Pre-treatment: Polishing, followed by etching in boiling HCl/HNO3 (3:1) for 2 hours, and annealing at 680 °C for 20 min.
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Homoepitaxial Layer Synthesis (MPCVD):
- Target Layer: Low-impurity intrinsic (i-layer) diamond.
- Equipment: Plassys BJS 150 CVD system.
- Substrate Temperature: 850 ± 15 °C.
- Microwave Power: 2.7 kW.
- Gas Mixture: H2/CH4 ratio of 24/1.
- Gas Pressure: 180 ± 5 mbar.
- Growth Rate: ~1.3 µm/h.
- Gas Purity: Total impurities in gas mixture < 5 ppb (relative to carbon).
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Device Fabrication (Schottky Diode):
- Ohmic Contact (Bottom): Ti (20 nm) / Pt (100 nm), annealed at 700 °C.
- Surface Treatment: Annealing at 650 °C followed by SF6 plasma treatment (20 min) to achieve fluorine termination for barrier height uniformity.
- Schottky Contact (Top): Pt (< 20 nm thick), deposited via magnetron sputtering (Area: 9 mm2).
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”6CCVD is uniquely positioned to supply the advanced diamond materials necessary to replicate and significantly improve upon the results of this betavoltaic research, particularly by mitigating the structural defects identified as the primary failure mechanism.
Applicable Materials
Section titled “Applicable Materials”The research highlights the critical need for high-quality, low-defect SCD material for the homoepitaxial layer and the n+ substrate.
| Research Requirement | 6CCVD Material Solution | Technical Advantage |
|---|---|---|
| Low-Defect Substrates | Optical Grade SCD (001) | Our MPCVD growth process yields SCD with inherently lower defect densities than typical HPHT material, directly addressing the high leakage issue observed with 300 ppm N substrates. |
| High-Purity i-Layer | High-Purity SCD (Undoped) | We guarantee ultra-high purity material for the intrinsic layer, essential for maximizing charge collection efficiency and minimizing recombination centers. |
| Doped Layers (n-type) | Custom N-Doped SCD | While the paper used N-doped HPHT, 6CCVD can provide precisely controlled N-doping in MPCVD SCD, allowing for optimized n+ layers with superior crystalline quality. |
| Future PiN Structures | Heavy Boron Doped SCD (BDD) | To achieve the higher efficiency (up to 29%) targeted by PiN structures, 6CCVD supplies highly conductive BDD (p-type) layers and substrates up to 500 µm thick. |
Customization Potential
Section titled “Customization Potential”6CCVD’s in-house engineering and fabrication capabilities directly support the complex requirements of advanced diamond device manufacturing.
- Custom Dimensions: While the paper used small 3.5 x 3.5 mm2 samples, 6CCVD can supply SCD plates up to 10 mm thick and PCD wafers up to 125 mm in diameter, enabling scaling and high-throughput device fabrication.
- Precision Thickness Control: We offer precise control over homoepitaxial layer thickness, from 0.1 µm to 500 µm, crucial for optimizing the i-layer width relative to the beta particle penetration depth.
- Advanced Metalization Services: The device requires specific Ti/Pt ohmic contacts and thin Pt Schottky contacts. 6CCVD offers internal metalization capabilities including Au, Pt, Pd, Ti, W, and Cu, allowing researchers to integrate custom contact schemes directly onto the diamond wafer, streamlining the fabrication process.
- Surface Quality: Achieving uniform Schottky barrier height relies on excellent surface quality. 6CCVD provides SCD polishing to Ra < 1 nm and inch-size PCD polishing to Ra < 5 nm, ensuring optimal surface preparation for subsequent plasma treatment and metal deposition.
Engineering Support
Section titled “Engineering Support”6CCVD’s in-house PhD team specializes in optimizing CVD growth recipes for specific electronic and radiation detection applications. We can assist researchers in:
- Material Selection: Consulting on the optimal substrate type (HPHT vs. MPCVD) and doping concentration (N or B) required to minimize leakage current and maximize efficiency in radioisotope energy converters.
- Recipe Transfer: Assisting with the transfer of complex homoepitaxial growth parameters (like the 850 °C, 2.7 kW recipe used here) to achieve high-quality, low-defect layers on larger substrates.
- Defect Mitigation: Providing advanced characterization data (e.g., dislocation mapping) to ensure the supplied material meets the strict 103-105 cm-2 defect density requirement for effective betavoltaic operation.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
In this paper, we study the formation and properties of diamond structures designed to convert the beta decay energy of the radioactive isotope 63Ni into electrical energy. Diamond substrates with different nitrogen concentrations (300 ppm and 60 ppm) were grown using the temperature gradient high-pressure thermonuclear technique (TG-HPHT). Analysis showed that a high nitrogen content leads to a significant increase in the number of structural defects in the substrates. Homoepitaxial layers with a low impurity content were synthesized using chemical vapor deposition on the diamond substrates. Then n-type Schottky diodes were manufactured by metal contacts deposition. The electrical properties of the diodes were studied when exposed to beta radiation. It was shown that substrates with a high nitrogen concentration inherit structural defects, which lead to high leakage currents and make such substrates unsuitable for creating efficient energy converters. At the same time, substrates with a nitrogen concentration of 60 ppm provide low leakage current and efficient energy conversion at temperatures up to 500 °C. The maximum electrical power was 170 pW with an efficiency of about 1%. The results demonstrate the importance of optimizing the nitrogen doping level and the crystalline quality of the substrates for creating efficient and durable radioisotope energy converters. For citation: Tarelkin S.A., Kornilov N.V., Kuznetsov M.S., Luparev N.V., Martyushov S.Yu., Timoshenko V.O. Features of the technology of homoepitaxial chemical deposition of thin diamond layers on a nitrogen-doped single-crystal diamond substrate. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2025. V. 68. N 9. P. 60-65. DOI: 10.6060/ivkkt.20256809.11y.