Development of high temperature, radiation hard detectors based on diamond

At a Glance

Metadata	Details
Publication Date	2016-06-26
Journal	Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
Authors	Alex Metcalfe, George R. Fern, P. R. Hobson, Terry G. Ireland, Ali Salimian
Institutions	Micron Semiconductor (United Kingdom), Schlumberger (France)
Citations	10
Analysis	Full AI Review Included

Technical Analysis of Diamond Radiation Detectors for High-Temperature Environments

Executive Summary

This documentation analyzes the research detailing the development of Single Crystal Diamond (SCD) detectors engineered for high-temperature (> 200°C) and radiation-hard applications, specifically focusing on spectroscopic detection of neutrons and gamma-rays.

High-Temperature Validation: Successful development and preliminary testing of specialized metallization schemes validate the stable operation of SCD detectors at 100°C, aiming for operational viability beyond 200°C.
Leakage Current Reduction: The proprietary high-temperature metallization drastically improved contact quality, reducing the detector leakage current by a factor of approximately 45 (from 0.63 pA to 0.014 pA at 100 V).
Spectroscopic Stability: Detectors demonstrated the capability to clearly resolve the triple alpha peaks (²⁴¹Am, ²³⁹Pu, ²⁴⁴Cm) with minimal spectral shift, confirming performance stability at 100°C.
Thermal Neutron Enhancement: Monte Carlo modeling (FLUKA/MCNPv6) confirms that the addition of conversion media (e.g., Boron) is crucial for thermal neutron detection, identifying an optimal planar converter thickness of approximately 3 µm.
3D Geometry Optimization: Simulations showed that transitioning from simple planar geometry to complex 3D structures (square ridge trenches) results in a projected 4.2 times improvement in thermal neutron detection efficiency.
Material Basis: The work relies exclusively on high-quality, electronic-grade Single Crystal Diamond substrates, reinforcing the need for reliable, high-purity MPCVD diamond material.

Technical Specifications

The following hard data points were extracted from the experimental and simulated results:

Parameter	Value	Unit	Context
Target Operational Temperature	> 200	°C	Required minimum operating temperature
Demonstrated Stable Temperature	100.0	°C	Temperature validated using alpha spectroscopy
High Temperature Contact Leakage	0.014	pA	Measured at 100 V bias
Standard Contact Leakage	0.63	pA	Measured at 100 V bias
Bias Voltage (High Temp Test)	300	V	Used during the high temperature 100°C test
Bias Voltage (Standard Test)	75	V	Used during the standard 100°C test
Optimal Planar Converter Thickness	≈ 3	µm	For maximizing thermal neutron counting efficiency (Figure 5)
Simulated Efficiency Improvement (3D vs. Planar)	4.2	times	Achieved using square ridge trench geometry (Figure 8)
Neutron Modeling Range (Fast)	< 20	MeV	Upper energy limit for FLUKA low energy neutron transport
Diamond Substrate Thicknesses Modeled	100, 200, 300, 400, 500	µm	Range used in gamma signal contribution simulations

Key Methodologies

The experimental approach focused on fabricating highly stable contacts on electronic-grade SCD and validating performance under elevated temperatures, complemented by advanced Monte Carlo modeling.

I. Detector Fabrication & Preparation

Substrate Selection: Utilized commercially available, electronic-grade Single Crystal Diamond (SCD) substrates.
Contact Development: Proprietary high-temperature metallization schemes were deposited using vacuum facilities (metal stacks chosen to ensure good ohmic contact and adhesion, noting that Pt was found unsuitable in similar prior work).
Physical Integration: Sensors were mounted onto a test PCB attached to a copper block equipped with an AlN heater element for temperature regulation.

II. Experimental Testing Parameters

Environment: Tests conducted in a turbopump-equipped vacuum chamber at a pressure of < 5x10^-4 mbar.
Temperature Control: External temperature controller (Lakeshore 331) maintained the copper block/sensor assembly at controlled temperatures up to 100°C.
Readout Chain: Standard nuclear instrumentation was employed:
- Preamp (Canberra model 2004)
- NIM Shaping Amplifier (Canberra model 2021)
- Multichannel Analyzer (Canberra Eagle Plus)
Radiation Source: A small triple alpha source (²⁴¹Am, ²³⁹Pu, ²⁴⁴Cm, 1 kBq activity each) was used to assess spectroscopic stability.

III. Simulation and Optimization

Radiation Transport Codes: Full simulation of particle interactions and energy deposition was carried out using two major integrated radiation transport packages: FLUKA2011 and MCNPv6.
Conversion Media Modeling: Initial models included planar sandwich geometries with Boron (specifically 100% ¹⁰B enriched) to simulate thermal neutron interaction.
Geometry Modeling: Models were extended to simulate 3D patterned surfaces (specifically square ridge trenches filled with conversion media) to assess gains in efficiency and position sensitivity.

6CCVD Solutions & Capabilities

6CCVD, as an expert material scientist and technical engineer specializing in MPCVD diamond, is uniquely positioned to supply the high-purity substrates and advanced processing required to replicate and extend this high-temperature detector research.

Research Requirement	6CCVD Solutions & Capabilities	Technical Value Proposition
High-Purity Substrates	Optical Grade/Electronic Grade Single Crystal Diamond (SCD): Standard and custom thicknesses from 0.1 µm up to 500 µm.	Provides the foundational material required for radiation hardness, low intrinsic background noise, and superior carrier transport essential for high-quality detectors.
Custom High-Temperature Contacts	Advanced Custom Metalization Services: In-house deposition of refractory metals and multi-layer stacks including Ti, Pt, Au, Pd, W, and Cu.	We can engineer and deposit the proprietary contact schemes required to achieve extremely low leakage current (0.014 pA demonstrated) and mechanical stability at temperatures > 200°C.
Conversion Media Integration	Boron-Doped Diamond (BDD) Films and Substrates: Available in both SCD and PCD format, allowing for heavy doping profiles.	Facilitates the integration of neutron converter analogues (e.g., Boron) either as films or as part of the detector material, stabilizing the interface and optimizing the required ≈ 3 µm conversion thickness.
3D Structured Surfaces (4.2x Gain)	Precision Laser Micromachining and Plasma Etching: In-house capability for custom patterning, deep etching, and producing high-aspect ratio features like the “square ridge trenches.”	Allows researchers to fabricate the complex 3D substrate geometry necessary to achieve the simulated 4.2x increase in thermal neutron detection efficiency without relying on fragile external coatings.
Large-Area Requirements	Custom Dimensions: SCD/PCD wafers and plates available up to 125mm in size.	Supports the transition from R&D prototypes to large-area functional devices or sensor arrays, especially valuable for large-scale neutron dosimetry applications.
Surface Finish Criticality	Ultra-Fine Polishing: Standard polishing to Ra < 1 nm (SCD) or Ra < 5 nm (PCD).	Ensures the surface quality maximizes carrier collection efficiency and minimizes the surface defects that contributed to high leakage current in the “Standard Metallisation” contacts.
Global R&D Support	Expert Engineering Support & Global Shipping: DDU default global shipping with DDP available.	6CCVD’s in-house PhD team can assist with material selection, doping level optimization, and geometric consultation for similar High-Temperature Neutron and Gamma Detection projects.

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

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.nima.2016.06.091

References

2010 - Investigation of mask selectivities and diamond etching using microwave plasma-assisted etching [Crossref]
2014 - The fluka code developments and challenges for high energy and medical applications [Crossref]
2012 - Initial mcnp6 release overview [Crossref]
2012 - Spectrometric performances of monocrystalline artificial diamond detectors operated at high temperature [Crossref]
2009 - A single-crystal diamond-based thermal neutron beam monitor for instruments at pulsed neutron sources [Crossref]
2012 - Monte Carlo simulations of multiplexed electronic grade cvd diamond for neutron detection [Crossref]