Comparison of Neutron Detection Performance of Four Thin-Film Semiconductor Neutron Detectors Based on Geant4

At a Glance

Metadata	Details
Publication Date	2021-11-27
Journal	Sensors
Authors	Zhongming Zhang, Michael D. Aspinall
Institutions	Lancaster University
Citations	5
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for Neutron Detection

This document analyzes the research paper “Comparison of Neutron Detection Performance of Four Thin-Film Semiconductor Neutron Detectors Based on Geant4” to highlight the superior performance of diamond and connect the material requirements directly to 6CCVD’s advanced MPCVD diamond capabilities.

Executive Summary

The simulation study validates Single Crystal Diamond (SCD) as the premier material for next-generation, thin-film semiconductor neutron detectors designed for extreme environments (high temperature, high radiation flux).

Superior Material Performance: Diamond demonstrated the best overall performance in thickness optimization, gamma rejection capability, and Electron Collection Efficiency (ECE) compared to SiC, Ga${2}$O${3}$, and GaN.
Optimal Thin-Film Requirement: The optimal SCD thickness required for maximum detection efficiency is extremely thin, ranging from 0.7 µm to 9.9 µm, depending on the converter layer (B$_{4}$C or LiF) and Low-Level Discriminator (LLD) setting.
Radiation Hardness: Diamond exhibits excellent radiation resistance, achieving a low Displacement Per Atom (DPA) value of 1.30 x 10^-20 under 1 MeV neutron flux, second only to GaN.
High Efficiency: SCD maintains high ECE (approaching 100%) even at low applied voltages (5 V), due to its high electron mobility (≈2000 cm²/V·s) and long carrier lifetime (≈2 µs).
Gamma Rejection: All tested materials met the intrinsic gamma detection efficiency requirement of < 10^-6, confirming their suitability for high-flux environments where gamma background is a concern.
6CCVD Advantage: 6CCVD specializes in the high-purity MPCVD SCD required to replicate and advance this research, offering precise thickness control (0.1 µm to 500 µm) and custom metalization for robust diode fabrication.

Technical Specifications

The following hard data points were extracted from the simulation results, focusing on the performance characteristics of Diamond (SCD).

Parameter	Value	Unit	Context
SCD Band Gap	5.5	eV	Wide band gap semiconductor
SCD Electron Mobility (µ)	≈2000	cm²/V·s	Highest among tested materials
SCD Electron Lifetime (τ)	≈2	µs	Critical for Charge Collection Efficiency (CCE)
Optimal SCD Thickness (B$_{4}$C, 300 keV LLD)	0.7	µm	Thinnest optimized film thickness
Optimal SCD Thickness (LiF, 900 keV LLD)	9.9	µm	Thicker LLD/Converter combination
Threshold Displacement Energy (E$_{d}$)	35	eV	Measure of lattice stability
Displacement Per Atom (DPA)	1.30 x 10^-20	DPA x cm²/incident particles	Radiation hardness (1 MeV neutron flux)
Average PKA Energy	134.30	keV	Primary Knock-on Atom energy
Minimum Gamma Rejection Efficiency	< 10^-6	Pulses/incident neutrons	Required to avoid ‘false-positive’ counts
Active Detector Area (Simulated)	1	cm²	Standard simulation geometry

Key Methodologies

The simulation utilized Geant4 to model the intrinsic thermal neutron detection efficiency, gamma rejection, radiation hardness, and electron collection efficiency (ECE) of thin-film semiconductor diodes.

Detector Structure: Two-layer thin-film diode structure consisting of an upper converter layer (B${4}$C or LiF) and a bottom semiconductor layer (Diamond, SiC, Ga${2}$O$_{3}$, or GaN).
Simulation Tool: Geant4 (version 10.7) was used, employing the FTFP_BERT_HP physics list for high-precision neutron modeling (elastic/inelastic scattering, capture, fission).
Source Parameters:
- Neutron Energy: 0.025 eV (thermal) for thickness optimization and gamma resistance studies.
- Neutron Energy: 1 MeV for radiation hardness (PKA/DPA) studies.
- Particle Counts: 5 x 10⁷ neutrons and 1 x 10⁸ gammas per simulation run.
Converter Layer Optimization: Optimal converter layer thicknesses were fixed based on LLD: B$_{4}$C (2.6 µm for 300 keV LLD) and LiF (30.6 µm for 300 keV LLD).
Semiconductor Optimization: Semiconductor thickness was continuously varied to find the point where detection efficiency asymptoted to a constant maximum.
Radiation Hardness Calculation: Primary Knock-on Atom (PKA) energy spectra were simulated, and Displacement Per Atom (DPA) was calculated using an early atomic displacement model based on kinetic energy transfer.
Charge Collection: Electron Collection Efficiency (ECE) was calculated using the single carrier Hecht Equation under applied bias voltages ranging from 5 V to 100 V.

6CCVD Solutions & Capabilities

The research confirms that high-purity, low-defect Single Crystal Diamond (SCD) is the optimal material for high-performance neutron detectors operating in extreme environments. 6CCVD is uniquely positioned to supply the precise material specifications required to transition this simulation work into fabricated devices.

Applicable Materials

To replicate or extend this research, engineers require the highest quality SCD material, characterized by low defect density to ensure maximum carrier lifetime (τ) and mobility (µ), which directly translates to high ECE/CCE.

Research Requirement	6CCVD Material Solution
Material: High-Purity Diamond for Extreme Environments	Optical Grade Single Crystal Diamond (SCD)
Doping: Intrinsic (i-type) semiconductor layer	Undoped SCD (High Resistivity)
Alternative: Large-area, cost-effective arrays	High-Quality Polycrystalline Diamond (PCD)
Converter Layer: B$_{4}$C or LiF integration	SCD/PCD Substrates with Polished Surface (Ra < 1 nm)

Customization Potential

The study emphasizes the critical role of precise, thin-film geometry. 6CCVD’s advanced MPCVD growth and fabrication capabilities directly address these needs:

Research Specification	6CCVD Customization Capability
Thickness Control (0.7 µm to 9.9 µm)	Precision SCD Thickness: We offer SCD films from 0.1 µm up to 500 µm, ensuring the exact sub-micron thickness required for optimal detection efficiency and minimal self-absorption.
Diode Fabrication (Contacts)	Custom Metalization: We provide in-house deposition of standard contact metals (e.g., Ti/Pt/Au, W, Cu) essential for creating robust Schottky or Ohmic contacts on the SCD diode structure.
Detector Size (1 cm² active area)	Custom Dimensions & Sizing: We supply SCD wafers and large-area PCD plates up to 125mm. Precision laser cutting services are available to achieve custom geometries and array configurations.
Surface Quality (High ECE/CCE)	Ultra-Smooth Polishing: Our SCD material achieves surface roughness of Ra < 1 nm, minimizing surface defects that could trap carriers and degrade charge collection efficiency.

Engineering Support

The transition from simulation (Geant4) to fabrication requires expert knowledge in material selection, surface preparation, and contact engineering.

Radiation Hardness Projects: 6CCVD’s in-house PhD team specializes in material science for extreme environments. We can assist researchers in selecting the optimal SCD grade and thickness to maximize radiation hardness (low DPA) and maintain high ECE for similar reactor monitoring and nuclear fusion projects.
CCE Optimization: We provide consultation on surface termination and metalization recipes to ensure low-resistance contacts, maximizing the charge collection efficiency (CCE) required for low-bias or zero-bias operation, as suggested by the high ECE performance of SCD.

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

View Original Abstract

Third-generation semiconductor materials have a wide band gap, high thermal conductivity, high chemical stability and strong radiation resistance. These materials have broad application prospects in optoelectronics, high-temperature and high-power equipment and radiation detectors. In this work, thin-film solid state neutron detectors made of four third-generation semiconductor materials are studied. Geant4 10.7 was used to analyze and optimize detectors. The optimal thicknesses required to achieve the highest detection efficiency for the four materials are studied. The optimized materials include diamond, silicon carbide (SiC), gallium oxide (Ga2O3) and gallium nitride (GaN), and the converter layer materials are boron carbide (B4C) and lithium fluoride (LiF) with a natural enrichment of boron and lithium. With optimal thickness, the primary knock-on atom (PKA) energy spectrum and displacements per atom (DPA) are studied to provide an indication of the radiation hardness of the four materials. The gamma rejection capabilities and electron collection efficiency (ECE) of these materials have also been studied. This work will contribute to manufacturing radiation-resistant, high-temperature-resistant and fast response neutron detectors. It will facilitate reactor monitoring, high-energy physics experiments and nuclear fusion research.

Tech Support

Original Source

DOI: https://doi.org/10.3390/s21237930

References

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