Синтез CVD-алмаза детекторного качества для радиационно-стойких детекторов ионизирующего излучения
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2022-01-01 |
| Journal | Журнал технической физики |
| Authors | А.В. Красильников, Н.Б. Родионов, А.П. Большаков, В.Г. Ральченко, С.К. Вартапетов |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This study reports the successful synthesis and characterization of high-quality homoepitaxial Chemical Vapor Deposition (CVD) diamond films specifically designed for radiation-hardened detectors.
- Core Achievement: Detector-grade CVD diamond films (70-80 µm thick) were grown using a modified ARDIS-300 Microwave (MW) plasma reactor on highly boron-doped (p-type) HPHT substrates.
- Purity and Quality: Experimental analysis confirmed the nitrogen impurity concentration (Ns0) in the epitaxial layer is exceptionally low, estimated to be less than 50 ppb.
- Charge Collection Efficiency (CCE): The synthesized detectors demonstrated high CCE, reaching 94% when exposed to 5.5 MeV alpha particles (Sample B21) under an applied field of ~4 V/µm.
- Neutron Detection Capability: High CCE (up to 91%) was achieved under 14.7 MeV neutron flux, confirming the material’s suitability for uniform volume charge generation applications.
- Structural Correlation: Structural perfection, measured by the narrowest Raman FWHM (2.2 cm-1 for B21), correlated directly with the highest CCE, emphasizing the importance of minimizing extended defects.
- Defect Analysis: Photoluminescence (PL) spectra showed NV0 and NV- defect centers, with the lowest PL intensity observed in the highest-performing sample (B21).
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Film Thickness (d) | 70-80 | µm | Homoepitaxial CVD films (B21, B22, B23) |
| Substrate Type | HPHT (100) | - | Boron-doped (p-type) |
| Boron Concentration (Substrate) | ~100 | ppm | HPHT Substrate |
| Nitrogen Concentration (Film) | <50 | ppb | Estimated Ns0 concentration via 270 nm absorption |
| Max CCE (Alpha Particles) | 94 | % | Sample B21, 5.5 MeV 241Am source, 4 V/µm field |
| Max CCE (Neutrons) | 91 | % | Sample B21, 14.7 MeV neutron flux |
| Estimated Energy Resolution (ΔE/E) | 1.7-2.5 | % | Corrected for source/air broadening |
| Raman FWHM (B21) | 2.2 | cm-1 | Structural quality indicator (lower is better) |
| Substrate Temperature (Ts) | 940-965 | °C | During CVD growth |
| Reactor Pressure (P) | 170 | Torr | Typical synthesis pressure |
| Methane Concentration [CH4] | 4 | % | In H2/CH4 gas mixture |
| Growth Rate (GR) | 3.0-4.0 | µm/h | Typical synthesis rate |
| Reactor Type | ARDIS-300 | - | Modified MW Plasma CVD (2.45 GHz) |
Key Methodologies
Section titled “Key Methodologies”The synthesis and characterization relied on highly controlled CVD processes and advanced optical and electrical testing:
- CVD Reactor Optimization: The ARDIS-300 MW plasma reactor was modified to achieve ultra-low atmospheric leakage (< 2.5 · 10-6 Torr · 1/s), ensuring background nitrogen concentration in the gas phase remained low (estimated < 2 ppm N2).
- Substrate Preparation: Conductive p-type HPHT diamond substrates were chemically cleaned (boiling in K2Cr2O7/H2SO4) and thermally annealed (590 °C) to remove non-diamond carbon phases and surface contaminants prior to growth.
- Epitaxial Growth: Homoepitaxial films were grown using H2/CH4 mixtures (4% CH4) at high temperatures (940-965 °C) and 170 Torr pressure, achieving thicknesses of 70-80 µm.
- Contact Deposition: Platinum (Pt) contacts (35 nm thick) were deposited via magnetron sputtering at 250 °C to form the metal-semiconductor-metal (MSM) detector structure.
- Structural Characterization (Raman): Phase purity was confirmed by the single diamond peak at 1332.5 cm-1. FWHM measurements (2.2-2.7 cm-1) were used to quantify crystalline perfection and internal stress.
- Impurity Characterization (PL/Absorption): Photoluminescence (PL) was used to monitor NV0 (575 nm) and NV- (638 nm) defect centers. Optical absorption at 270 nm was used to estimate the concentration of single substitutional nitrogen (Ns0 < 50 ppb).
- Alpha Particle Testing: CCE and energy spectra were measured using a 241Am source (5.5 MeV) in both air and vacuum, focusing on charge collection in the shallow, near-anode region.
- Neutron Spectroscopy: Detector response was measured under 14.7 MeV neutron flux (from an ING-07T generator) to assess CCE under conditions of uniform volume ionization (via C(n,n)C, C(n,α)2α, and C(n,α)Be reactions).
Commercial Applications
Section titled “Commercial Applications”The synthesis of high-quality, detector-grade CVD diamond is critical for several high-demand, radiation-intensive fields:
- Fusion Energy Research (ITER): Diamond detectors are essential for real-time spectrometry and flux monitoring of 14 MeV neutrons generated during Deuterium-Tritium (D-T) fusion reactions, due to their unparalleled radiation hardness.
- High Energy Physics (HEP): Used in particle accelerators and colliders (e.g., CERN) as beam monitors, tracking detectors, and luminosity monitors, where high spatial resolution and extreme radiation tolerance are required.
- Nuclear and Security Applications: Employed in neutron and gamma ray detection systems for nuclear safeguards, reactor monitoring, and homeland security, offering superior performance compared to conventional semiconductors in harsh environments.
- Medical Dosimetry: Used in advanced radiation therapy (e.g., hadron therapy) for precise measurement of high-dose radiation fields due to diamond’s tissue equivalence and stability.
- High-Power Electronics: The low-defect, high-purity material developed for detectors is also foundational for high-voltage and high-frequency diamond electronic devices, leveraging diamond’s high breakdown field and thermal conductivity.
View Original Abstract
An advanced microwave plasma reactor ARDIS 300 was used to synthesize homoepitaxial structures of monocrystal diamond films at Project Center ITER. High-quality epitaxial diamond films were grown on boron-doped monocrystal diamond substrates using microwave plasma-assisted chemical vapor deposition from methane-hydrogen mixture. Structural and impurity perfection of diamond films were characterized by Raman spectroscopy, photoluminescence, and optical absorption. Prototypes of radiation detectors were created on the basis of grown diamond films with thickness 70-80 μm. The p-type substrate with boron concentration ~100 ppm served as an electrical contact. Detectors were irradiated by 5.5 MeV α-particles and 14.7 MeV neutrons, corresponding pulse height spectra were measured and detector sensitivities were determined. Charge collection efficiency for synthesized diamond was shown to achieve 94% and 91% when ~4 V/m electric field applied.