CVD-synthesis of detector quality diamond for radiation hardness detectors of ionizing radiation

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

Technical Documentation & Analysis: CVD Diamond for Radiation Hardness Detectors

This document analyzes the research paper “CVD-synthesis of detector quality diamond for radiation hardness detectors of ionizing radiation” and maps the material requirements and experimental successes to the advanced capabilities offered by 6CCVD.

Executive Summary

The research successfully demonstrates the synthesis of high-quality, detector-grade single crystal diamond (SCD) films via Microwave Plasma Chemical Vapor Deposition (MPCVD) for use in radiation-hardened detectors.

High Charge Collection Efficiency (CCE): Synthesized SCD films achieved CCE up to 94% for 5.5 MeV alpha particles and 91% for 14.7 MeV neutrons, confirming suitability for high-energy physics applications.
Ultra-High Purity: The epitaxial films exhibited ultra-low nitrogen impurity concentrations, experimentally confirmed to be below 50 ppb, which is critical for minimizing charge trapping sites.
Thin-Film Detector Design: Detectors utilized thin (70-80 µm) undoped SCD active layers grown on highly Boron-Doped (p-type) HPHT substrates, enabling reduced bias voltage requirements.
Structural Perfection: Material quality was verified by Raman spectroscopy, yielding a narrow FWHM of 2.2 cm^-1, correlating directly with enhanced charge collection performance.
Radiation Hardness: The detectors demonstrated high stability of parameters under continuous flux of both alpha particles and neutrons.
Methodology: Homoepitaxial growth was performed in a modernized ARDIS-300 MPCVD reactor using optimized CH₄/H₂ mixtures and precise temperature control (T_s ~940 °C).

Technical Specifications

The following hard data points were extracted from the synthesis and performance characterization of the detector-grade diamond films (Samples B21, B22, B23).

Parameter	Value	Unit	Context
Charge Collection Efficiency (CCE)	94	%	Best result (B21), 5.5 MeV alpha particles
Charge Collection Efficiency (CCE)	91	%	Best result (B21), 14.7 MeV neutrons
Epitaxial Film Thickness (d)	70 - 80	µm	Active detector layer
Substrate Boron Concentration	~100	ppm	HPHT p-type conducting layer
Epitaxial Nitrogen Concentration (N_s)	< 50	ppb	Detector-grade purity requirement
Raman Peak FWHM (Film B21)	2.2	cm^-1	Indicator of crystalline perfection
Required Electric Field	~4	V/µm	Applied bias for maximum CCE
Substrate Temperature (T_s)	940 - 1050	°C	CVD growth range
Reactor Pressure (p)	140 - 170	Torr	CVD growth range
Methane Concentration [CH₄]	1.5 - 4	%	Gas mixture composition
Metal Contact Material	Platinum (Pt)	35 nm	Sputtered electrode thickness
Energy Resolution (Alpha, B21)	1.69	%	Measured at 88 keV

Key Methodologies

The synthesis of high-quality, detector-grade SCD films relied on stringent control over the MPCVD environment and material preparation.

Reactor and Vacuum Control: Epitaxial films were grown in a modernized ARDIS-300 MPCVD reactor (2.45 GHz). High vacuum (5 x 10^-7 Torr) and minimized atmospheric leakage (2.5 x 10^-6 Torr·l/s) were maintained to ensure ultra-low background nitrogen impurity.
Substrate Selection: Conducting HPHT single-crystal diamond substrates (4.5 x 4.5 x 0.5 mm, (100) orientation) heavily doped with boron (~100 ppm) were used as the back contact.
Substrate Pre-treatment: Substrates were annealed in air (590 °C) to remove non-diamond carbon, followed by boiling in potassium bichromate/concentrated sulfuric acid (K₂Cr₂O₇/H₂SO₄) solution to remove surface contaminants.
Gas Purity: Ultra-high purity reagents were used (99.99999% O₂, 99.9999% CH₄). The N/C ratio in the gas phase was maintained around 100 ppm.
CVD Growth Parameters: Typical growth conditions included 170 Torr pressure, 4% CH₄ concentration, and substrate temperatures around 940 °C, resulting in growth rates of 3.0-4.0 µm/h.
Post-Growth Processing: One sample (B23) was ground and polished to reduce the epitaxial layer thickness by 20 µm. Chemical cleaning (boiling in K₂Cr₂O₇/H₂SO₄) was performed to remove amorphous carbon.
Contact Deposition: Solid 35 nm thick Platinum (Pt) contacts were deposited onto both the growth surface and the conducting substrate via magnetron sputtering at 250 °C.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to support and advance research into radiation-hardened diamond detectors by providing materials and services that meet or exceed the specifications required in this study.

Applicable Materials

To replicate or extend this high-performance detector research, 6CCVD recommends the following materials:

Optical Grade SCD (Single Crystal Diamond): Required for the active layer. Our Optical Grade SCD ensures the ultra-low nitrogen concentration (< 50 ppb) and high crystalline perfection (Raman FWHM < 2.5 cm^-1) necessary to achieve CCE > 90%.
- Thickness Range: Available from 0.1 µm up to 500 µm, allowing precise control over the active volume (70-80 µm used in the paper).
Heavy Boron Doped Diamond (BDD) Substrates: Essential for the integrated conducting back contact. We supply BDD substrates (up to 10 mm thick) with controlled boron concentrations, providing the necessary p-type conductivity for thin-film epitaxy and electrode function.

Customization Potential

The success of these detectors relies on precise geometry and specialized contacts. 6CCVD offers comprehensive customization services:

Research Requirement	6CCVD Customization Service	Benefit to Client
Scaling Detector Area	Custom Plates/Wafers up to 125 mm (PCD) and large-area SCD.	Enables scaling from small research samples (4.5 x 4.5 mm) to industrial or large-scale physics detector arrays.
Electrode Fabrication	Custom Metalization: Internal deposition of Au, Pt, Pd, Ti, W, and Cu.	We can replicate the 35 nm Pt contacts used in the study or optimize multi-layer stacks (e.g., Ti/Pt/Au) for enhanced adhesion and conductivity.
Surface Preparation	Precision Polishing: Ra < 1 nm (SCD) and Ra < 5 nm (PCD).	Ensures the atomically smooth surface required to minimize charge trapping defects (NV centers) and maximize CCE, especially critical for thin-film devices.
Thickness Control	Precision SCD Growth: Thickness control down to 0.1 µm.	Allows engineers to precisely tune the active layer thickness (70-80 µm) to match the charge collection distance (CCD) and optimize bias voltage requirements.

Engineering Support

6CCVD’s in-house PhD team specializes in material science and device physics for diamond detectors. We can assist researchers and engineers with:

Material Selection: Guidance on selecting the optimal SCD purity grade and BDD doping level to maximize CCE and minimize leakage current for specific radiation detection projects (e.g., alpha, neutron, or high-load environments).
Process Optimization: Consultation on substrate preparation and post-growth processing techniques (like the acid boiling and polishing steps detailed in the paper) to ensure high structural perfection (low Raman FWHM).

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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

Tech Support

Original Source

DOI: https://doi.org/10.21883/tp.2022.04.53607.226-21