Characterization of the charge‐carrier transport properties of IIa‐Tech SC diamond for radiation detection applications

At a Glance

Metadata	Details
Publication Date	2015-07-15
Journal	physica status solidi (a)
Authors	M. Pomorski, Colin Delfaure, Nicolas Vaissière, H. Bensalah, Julien Barjon
Institutions	Centre National de la Recherche Scientifique, Université de Versailles Saint-Quentin-en-Yvelines
Citations	13
Analysis	Full AI Review Included

Technical Documentation and Analysis: High-Purity Single Crystal Diamond for Radiation Detection

This document analyzes the research paper, “Characterization of the charge-carrier transport properties of IIa-Tech SC diamond for radiation detection applications,” to extract key technical specifications and align them with the advanced MPCVD diamond solutions offered by 6CCVD.

Executive Summary

This paper validates the use of ultra-high purity, Single Crystal Diamond (SCD) grown by Chemical Vapor Deposition (CVD) for high-performance radiation detection, demonstrating charge-carrier transport metrics comparable to or exceeding current industry benchmarks.

Superior Carrier Transport: Full Charge Collection Efficiency (CCE) was achieved at ultra-low electric fields, reported as low as 0.11 V/µm, indicating exceptionally low defect and trapping density.
High Drift Velocities: Measured hole drift velocity of 53 µm/ns and electron drift velocity of 38 µm/ns (at 0.33 V/µm), confirming rapid charge extraction necessary for high-speed particle tracking.
Exceptional Purity: Cathodoluminescence (CL) spectroscopy confirmed extremely high material purity, with Boron acceptor concentration below the detection limit (estimated < 1 x 10¹³ cm^-3).
High Energy Resolution: Achieved relative resolution ΔE = FWHM/x_c of 0.8% for 5.486 MeV α-particles, demonstrating excellent uniformity and spectral quality, approaching metrics previously only seen in much thinner samples.
Operational Stability: Negligible space charge build-up, trapping, or polarization was observed during Transient Current Technique (TCT) and X-ray irradiation tests, confirming suitability for long-term, high-fluence environments.
Core Conclusion: The performance validates MPCVD SCD as a high-grade, commercially viable material for advanced high-energy physics, dosimetry, and nuclear monitoring applications.

Technical Specifications

Extracted quantitative data points characterizing the IIa-Tech SC diamond sample and its performance under radiation testing.

Parameter	Value	Unit	Context
Material Orientation	<100>	-	SC CVD Diamond
Sample Thickness (d)	890	µm	Detector active layer
Lateral Dimensions	3 x 3	mm²	Device size
Electrode Type	Aluminum (Al)	~200 nm	Sputtered parallel plate contacts
Minimum Full CCE Field	0.11	V/µm	Field required for saturation
Hole Drift Velocity (V_h)	53	µm/ns	Probed at 0.33 V/µm
Electron Drift Velocity (V_e)	38	µm/ns	Probed at 0.33 V/µm
Electron Saturation Velocity (V_sat,e)	2.63 x 10⁷	cm/s	Empirical fit parameter
Hole Saturation Velocity (V_sat,h)	1.57 x 10⁷	cm/s	Empirical fit parameter
Low Field Electron Mobility (µ_o,e)	4551 ± 500	cm²/Vs	Fitted transport metric
Low Field Hole Mobility (µ_o,h)	2750 ± 70	cm²/Vs	Fitted transport metric
α-Particle Energy	5.486	MeV	Am-241 TCT source
α-Particle Range	~14	µm	E-H pair generation depth
Energy Resolution (FWHM/x_c)	0.8	%	For 5.486 MeV α-particles
Boron Concentration (B)	< 1 x 10¹³	cm^-3	Below CL detection limit (at 8 K)

Key Methodologies

A concise sequence outlining the preparation, characterization, and core charge transport measurement techniques employed in the study.

Chemical Cleaning: Sample surfaces were cleaned in a hot acid solution (saturated H₂SO₄ + KNO₃) at 290 °C for 20 minutes to remove surface contaminants prior to metalization.
Contact Deposition: Parallel plate Al contacts (~200 nm thick) were deposited onto the cleaned diamond surfaces via magnetron sputtering using shadow masks.
Optical Characterization (CL): Cathodoluminescence (CL) spectroscopy was conducted at 8 K using a 10 keV electron beam to evaluate intrinsic band-edge emissions and identify deep defect signatures (N, B, Si centers), confirming ultra-high purity.
Transient Current Technique (TCT): TCT was performed using a spectroscopic grade Am-241 source (5.486 MeV α-particles). Due to the short range of the particles (~14 µm), TCT enabled separate evaluation of electron and hole transport parameters (drift velocity, trapping time).
TCT Signal Acquisition: Transient current waveforms were amplified using a broad-band amplifier (40 dB gain) and recorded on a 2 GHz bandwidth oscilloscope under DC bias supplied by a high-voltage power source.
Charge Collection Efficiency (CCE) Measurement: The integral of the transient current signals was measured as a function of bias voltage to determine the collected charge and confirm the electric field required for full CCE saturation.
Long-Term Stability Testing: Photocurrent induced by continuous X-ray exposure (50 keV, 0.5 mA) was monitored to assess detector stability, signal response, and the absence of space charge buildup or polarization effects.

6CCVD Solutions & Capabilities

This research confirms the potential of high-purity MPCVD SCD diamond for achieving state-of-the-art radiation detector performance. 6CCVD is uniquely positioned to supply and engineer materials necessary to replicate and advance this research, offering customized manufacturing flexibility.

Applicable Materials

The achieved low CCE threshold and high carrier velocity require ultra-high purity material. 6CCVD directly supplies the requisite intrinsic MPCVD material.

Primary Recommendation: Optical Grade Single Crystal Diamond (SCD)
- Purity: Guaranteed ultra-low nitrogen content (typically < 5 ppb), essential for minimizing deep traps that limit carrier lifetime and cause polarization/space charge buildup.
- Orientation: Available in standard <100> orientation used in this study, as well as <111> options upon request.
- Application Focus: Recommended for high-resolution dosimetry, particle spectroscopy (alpha, beta, high-energy X-ray), and high-stability monitoring devices.

Customization Potential

The experimental setup relied on specific dimensions and custom contact schemes. 6CCVD’s in-house engineering capabilities simplify the production of application-specific detector wafers.

Feature Described in Paper	6CCVD Customization Service	Technical Benefit
Specific Dimensions (3 x 3 mm²)	Precision Laser Cutting and Sizing: We provide custom cuts and dicing down to millimeter scale, ensuring alignment with specific detector assembly requirements (e.g., pixel detectors).	Enables integration into complex arrays and maximizes material yield for small sensors.
Thickness (890 µm)	Custom MPCVD Thickness: We supply SCD in highly precise thicknesses from 0.1 µm up to 500 µm, and substrates up to 10 mm, easily covering the ~900 µm requirement.	Supports optimization for different particle types (e.g., thin films for TCT/beam monitoring; thick substrates for high-energy dosimetry).
Metalization (Al Contacts)	In-House Electrode Deposition: Replication of the device contacts is simplified through our internal metalization capabilities, including Au, Pt, Pd, Ti, W, Cu, and Al (used in this study).	Ensures excellent adhesion, low resistivity, and uniform Schottky or ohmic contacts critical for reproducible charge transport measurements.
Surface Finish	Standard Ra < 1 nm Polishing (SCD): High-quality polishing is standard, minimizing surface defects that can interfere with contact formation and carrier trapping near the electrodes.	Ensures uniform electric fields and stable current signals, preventing the unstable responses (priming/overshoot) noted in lower-grade materials.

Engineering Support

This research demonstrates that minor variations in impurity levels (especially nitrogen and boron) critically impact charge transport parameters.

6CCVD’s in-house PhD team provides specialized engineering support to assist researchers and technical buyers in selecting and optimizing the precise material grade (purity, orientation, thickness) required for nuclear particle detection projects. We leverage our MPCVD growth expertise to minimize the defects responsible for carrier trapping, ensuring high mobility and stable CCE saturation characteristics confirmed by this analysis.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship high-performance diamond materials globally (DDU default, DDP available).

View Original Abstract

Single crystal (SC) diamond has since years demonstrated its interest for the fabrication of radiation detectors, especially where the material properties are providing superior interests with respect to the detection application. Among the industrial suppliers able to provide on a commercial basis high‐grade single crystal diamond, IIa‐Tech has recently appeared in the market as a new player. The aim of this paper is to assess the quality of one SC sample when characterized under α‐particles for the measurement of its carrier transport properties. We observed that full charge collection could be observed at biases as low as 0.11 V/μm with no space charge build‐up (conventionally typical bias values used are closer to 1 V/μm). Velocity reached values of 38 μm/ns and 53 μm/ns for electrons and holes, respectively (values probed at 0.33 V/μm). Similarly, the α detection spectrum displays a sharp line demonstrating the good uniformity of the material over its surface. By combining the measurements with more conventional optical observations such as birefringence and cathodoluminescence spectroscopy, it comes that the material demonstrates its ability to be used as a detector, with properties that can compare with the highest grade materials today available on the market.

Tech Support

Original Source

DOI: https://doi.org/10.1002/pssa.201532230

References

2003 - Luminescence from Optical Defects and Impurities in CVD Diamond, Thin‐Film Diamond I, Semiconductors and Semimetals Series