CVD-synthesis of detector quality diamond for radiation hardness detectors of ionizing radiation
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2022-01-01 |
| Journal | Журнал технической физики |
| Authors | Krasilnikov A.V., Rodionov N.B., Bolshakov A.P., Ralchenko V.G., Vartapetov S.K. |
| Institutions | Prokhorov General Physics Institute |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This study reports the successful synthesis and characterization of high-performance, radiation-hardened single-crystal diamond films using Chemical Vapor Deposition (CVD).
- Core Achievement: Homoepitaxial undoped diamond films (70-80 µm thick) were grown on boron-doped HPHT substrates using a modernized ARDIS-300 microwave plasma reactor.
- High CCE Performance: The best detector prototype (B21) achieved a Charge Collection Efficiency (CCE) of 94% under 5.5 MeV alpha particle irradiation (in vacuum) and 91% under 14.7 MeV neutron flux.
- Low Impurity Level: The epitaxial material demonstrated detector-grade purity, with the concentration of single substituting nitrogen atoms (Ns) estimated to be less than 50 ppb.
- Material Quality Correlation: Detector efficiency was directly correlated with crystalline perfection; CCE increased as the Raman peak Full Width at Half Maximum (FWHM) decreased (best FWHM: 2.2 cm-1).
- Radiation Hardness: The detectors exhibited high stability of parameters when detecting both alpha particles and neutrons, confirming suitability for high-radiation environments.
- Structure Design: The conducting boron-doped substrate (~100 ppm B) serves as the back electrical contact, enabling the use of thin epitaxial films as the active sensing layer.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Reactor Type | ARDIS-300 | N/A | Microwave Plasma CVD (2.45 GHz) |
| Epitaxial Film Thickness (B21) | 70 | µm | Active detector layer |
| Substrate Type | HPHT, Boron-doped | N/A | Used as back contact |
| Substrate Boron Conc. | ~100 | ppm | Equivalent to 1.76 x 1017 cm-3 |
| Film Nitrogen Conc. (Ns) | < 50 | ppb | Estimated maximum impurity level |
| Charge Collection Efficiency (CCE) | 94 | % | B21 film, 5.5 MeV alpha particles |
| CCE (Neutron Flux) | 91 | % | B21 film, 14.7 MeV neutrons |
| Electric Field Applied (CCE Test) | ~4 | V/µm | Required bias for high CCE |
| Energy Resolution (Alpha, B21) | 88 keV (1.69) | % | Measured in vacuum |
| Raman FWHM (B21) | 2.2 | cm-1 | Indicator of crystalline perfection |
| Growth Rate (B21) | 3.0 | µm/h | CVD deposition rate |
| Substrate Temperature (Ts) | 940 | °C | Synthesis condition for B21/B22 |
| Gas Pressure (P) | 170 | Torr | Synthesis condition for B21/B22/B23 |
| Methane Concentration ([CH4]) | 4 | % | Synthesis condition for B21/B22/B23 |
| Contact Material | Platinum (Pt) | N/A | 35 nm thickness, magnetron sputtered |
Key Methodologies
Section titled “Key Methodologies”- Reactor Modernization: Used a modernized ARDIS-300 reactor with reduced atmospheric leakage (leakage rate < 2.5 x 10-6 Torr·l/s) to ensure ultra-low background nitrogen impurity in the gas mixture (N2 concentration ~2 ppm).
- Substrate Selection: Conductive, boron-doped HPHT single-crystal diamond substrates (4.5 x 4.5 x 0.5 mm, (100) orientation) were used for homoepitaxy.
- Pre-Growth Cleaning: Substrates were rigorously cleaned: annealing in air (590 °C), boiling in potassium bichromate/concentrated sulfuric acid (H2SO4) solution, and ultrasonic treatment in isopropyl alcohol.
- CVD Synthesis: Epitaxial films (50-80 µm thick) were grown using microwave plasma-assisted CVD from a methane-hydrogen mixture.
- Typical parameters: Pressure 170 Torr, [CH4] 4%, Substrate Temperature 940 °C, Microwave Power 5500 W.
- Material Characterization:
- Structural Perfection: Raman spectroscopy confirmed single-line diamond structure (1332.5 cm-1) and measured crystalline perfection (FWHM).
- Impurity Analysis: Photoluminescence (PL) spectroscopy monitored nitrogen-vacancy (NV0 and NV-) defects. Optical absorption measured single substituting nitrogen (Ns) concentration (< 50 ppb).
- Detector Fabrication: Solid platinum contacts (35 nm) were deposited via magnetron sputtering at 250 °C onto the growth face and the conductive substrate face.
- Performance Testing:
- Alpha Detection: Amplitude spectra measured under 5.5 MeV alpha particles (241Am source) to determine CCE in the anode region.
- Neutron Detection: Amplitude spectra measured under 14.7 MeV neutron flux (ING-07T generator) to estimate CCE upon uniform electron-hole pair generation throughout the volume.
Commercial Applications
Section titled “Commercial Applications”The synthesized detector-grade diamond films are highly suitable for applications requiring extreme radiation hardness, high speed, and stability in harsh environments.
- High-Energy Physics (HEP) Experiments: Used as radiation-hardened ionization detectors in high-flux particle accelerators and colliders (e.g., future upgrades at CERN).
- Fusion Energy Research: Spectrometry of fast neutrons (14.7 MeV DT neutrons) in thermonuclear research facilities (e.g., ITER, JET, TFTR).
- Nuclear Instrumentation: High-load electronic modules and sensors for monitoring nuclear processes, capable of operating up to 700 °C.
- Compact Detector Design: Fabrication of thin-film detectors (tens of µm) allows for significantly reduced required bias voltage, leading to more compact and efficient detection systems.
- Neutron Dosimetry: Utilizing the C(n, α)Be reaction for highly accurate, stable neutron flux measurement.
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 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/μm electric field applied. Keywords: diamond films, epitaxy, diamond detector