High-temperature Operation Characteristics of Diamond Radiation Detectors

At a Glance

Metadata	Details
Publication Date	2025-05-22
Journal	Sensors and Materials
Authors	Masakatsu Tsubota, Takehiro Shimaoka, Yoshihiro J. Akashi, Shintaro Hirano, Akiyoshi Chayahara
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Temperature Diamond Detectors

Executive Summary

This research successfully demonstrates the stable, high-temperature operation of Single Crystal Diamond (SCD) radiation detectors, validating MPCVD diamond as the superior material for extreme environments.

Extreme Temperature Operation: SCD detectors maintained stable charge collection efficiency (CCE) and energy resolution up to 500 °C, significantly exceeding the operational limits of SiC and GaN devices.
Leakage Current Suppression: The critical challenge of increased leakage current at high temperatures was effectively solved using a photolithographically defined guard ring electrode structure.
Improved Charge Transport: The hole mobility-lifetime ($\mu\tau$) product showed considerable improvement with increasing temperature, reaching $2 \times 10^{-4}$ cm²/V at 500 °C, indicating enhanced carrier transport properties.
High Purity Requirement: The successful operation relied on electronics-grade SCD synthesized by MPCVD, characterized by extremely low nitrogen impurity levels (< part per billion).
Application Validation: This work confirms the viability of MPCVD SCD for critical high-dose, high-temperature applications, including fusion plasma diagnostics and nuclear reactor core monitoring.
Device Structure: The detector utilized a Ti/Pt metalization stack to form a stable TiC Schottky contact, crucial for high-temperature stability (stable up to 650 °C).

Technical Specifications

The following hard data points were extracted from the research paper, highlighting the performance and material requirements for high-temperature diamond detectors.

Parameter	Value	Unit	Context
Maximum Operating Temperature	500	°C	Stable detector operation demonstrated.
Diamond Band Gap	5.47	eV	Wide band gap enabling high-temperature use.
SCD Thickness (HU Sample)	85	µm	CVD layer thickness used for detection.
SCD Area (HU Sample)	5 x 5	mm²	Sample dimensions.
CVD Nitrogen Impurity Level	< part per billion	N/A	Required for electronics-grade performance.
Hole $\mu\tau$ Product (500 °C)	$2 \times 10^{-4}$	cm²/V	Peak value achieved at maximum temperature.
Electron Energy Resolution (500 °C)	0.8	%	Resolution in response to 5.486 MeV $\alpha$-particles.
Hole Energy Resolution (500 °C)	0.6	%	Resolution in response to 5.486 MeV $\alpha$-particles.
Leakage Current (500 °C, w/ GR)	~10	pA	Current at 2000 V/cm electric field, suppressed by guard ring.
Schottky Contact Metalization	Ti (50 nm) / Pt (50 nm)	nm	Stack used to form stable TiC interface.
TiC Formation Temperature	400	°C	Vacuum heating condition for stable interface.

Key Methodologies

The successful fabrication and testing of the high-temperature diamond detector relied on precise MPCVD synthesis and advanced device engineering techniques.

Material Synthesis: Homoepitaxial growth of Single Crystal Diamond (SCD) was performed using Microwave Plasma Chemical Vapor Deposition (MPCVD) on Type-IIa HP/HT substrates.
CVD Recipe: The growth utilized H₂ and 0.2% CH₄ mixed gases at 110 Torr pressure and a substrate surface temperature of 900 °C.
Substrate Reuse: A lift-off process was employed to separate the high-purity SCD growth layer (85 µm thick) from the expensive substrate, ensuring reproducibility and cost efficiency.
Surface Treatment: The diamond surface was changed from hydrogen-terminated to oxygen-terminated via dichromate treatment to decrease surface conductivity and minimize surface leakage current up to 300 °C.
Electrode Deposition: Metal electrodes were attached by vapor deposition. The active side used a Ti (50 nm) / Pt (50 nm) stack, forming a TiC Schottky contact after vacuum heating at 400 °C. The opposite side used a Pt (50 nm) electrode.
Guard Ring Fabrication: A guard ring electrode structure (4.0 mm radius, 0.3 mm width) was defined using photolithography to surround the 2.5 mm radius center electrode, specifically to suppress leakage current above 300 °C.
High-Temperature Testing: I-V and CCE measurements were conducted in a vacuum chamber up to 500 °C, using 5.486 MeV $\alpha$-particles from a ²⁴¹Am source.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials and custom fabrication services required to replicate and extend this high-temperature radiation detection research.

Applicable Materials

To achieve the low leakage current and high charge transport properties demonstrated in this paper, researchers require the highest purity diamond.

6CCVD Material	Specification Match	Relevance to Research
Electronics Grade Single Crystal Diamond (SCD)	Nitrogen concentration < 5 ppb.	Essential for minimizing deep-level defects (like the 1.7 eV N-V center) that cause charge trapping and increased leakage current at high temperatures.
Custom Thickness SCD Wafers	0.1 µm to 500 µm	Allows precise control over detector thickness (d) for optimizing CCE saturation and electric field (E) requirements in Hecht’s equation.
Optical Grade SCD	Ra < 1 nm polishing.	Provides the necessary surface quality for high-resolution photolithography required to define the guard ring structure.

Customization Potential

The device fabrication in this study relies heavily on specific dimensions and metal contacts. 6CCVD offers comprehensive services to meet these exact engineering requirements.

Custom Dimensions and Thickness: While the paper used 5 x 5 mm² samples, 6CCVD can supply SCD plates up to 10 x 10 mm and Polycrystalline Diamond (PCD) wafers up to 125 mm in diameter, allowing for scaling of detector arrays.
Precision Metalization Services: 6CCVD offers in-house vapor deposition capabilities for the exact electrode stack used: Ti/Pt (50 nm / 50 nm). We also offer other high-temperature refractory metals (W, Pd) suitable for stable contacts above the 650 °C carbonization limit of Ti/Pt.
Surface Preparation: We provide SCD wafers with controlled surface termination (hydrogen or oxygen) and ultra-smooth polishing (Ra < 1 nm) ready for immediate photolithographic patterning of complex electrode geometries, such as the critical guard ring structure.
Substrate Options: For applications requiring thicker support or specific thermal management, 6CCVD offers substrates up to 10 mm thick.

Engineering Support

The optimization of the $\mu\tau$ product and leakage current suppression at 500 °C requires deep material and device physics expertise.

High-Temperature Sensor Design: 6CCVD’s in-house PhD team specializes in material selection and device architecture for extreme environments, including high-temperature radiation detection and high-power electronics.
Charge Transport Optimization: We assist researchers in selecting the optimal SCD purity and thickness to maximize the mobility-lifetime product for specific carrier types (holes or electrons), crucial for replicating the improved hole transport observed in this study.
Custom Electrode Consultation: Our engineers can consult on advanced electrode designs, including multi-ring guard structures and alternative metalization schemes, to push operational limits beyond the 500 °C achieved here, targeting the 700 °C goal mentioned in the conclusion.

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

Tech Support

Original Source

DOI: https://doi.org/10.18494/sam5528