Ion Microprobe Study of the Polarization Quenching Techniques in Single Crystal Diamond Radiation Detectors

At a Glance

Metadata	Details
Publication Date	2022-01-05
Journal	Materials
Authors	M. Rodríguez-Ramos, Andreo Crnjac, D. Cosic, M. Jakšić
Institutions	Rudjer Boskovic Institute
Citations	8
Analysis	Full AI Review Included

Technical Documentation & Analysis: Polarization Quenching in sc-CVD Diamond Detectors

Executive Summary

This documentation analyzes the research on mitigating polarization effects in Single Crystal Chemical Vapor Deposition (sc-CVD) diamond radiation detectors (DDs). Polarization, caused by space charge accumulation, severely degrades Charge Collection Efficiency (CCE) in harsh environments.

Material Validation: High-purity, electronic-grade sc-CVD diamond is confirmed as an extraordinary candidate for radiation monitoring due to its large band gap (≈5.5 eV) and high radiation resistance (43 eV displacement energy).
Core Challenge Addressed: The study successfully tested four techniques—thermal excitation, bias switching (on/off), alternating bias, and optical excitation—to quench polarization and restore CCE.
Thermal Quenching Success: Heating the detector above 90 °C significantly reduced CCE degradation for holes, decreasing the drop from ≈60% (Room Temperature) to ≈13% (175 °C).
Bias Switching Efficacy: Turning off the bias while the ion beam remains continuous proved to be a satisfactory method for CCE recovery, attributed to recombination neutralizing trapped space charge.
Optical Quenching: Illumination with white light suppressed polarization induced by hole traps specifically in radiation-damaged regions, offering a standard method for recovery in compromised devices.
6CCVD Value Proposition: 6CCVD specializes in providing the high-purity SCD material, custom dimensions (up to 500 µm thickness used in the study), and custom metalization (W, Ti, Au, Pt) required to replicate and advance this critical research.

Technical Specifications

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

Parameter	Value	Unit	Context
Material Type	sc-CVD Diamond	N/A	Electronic Grade
Detector A Dimensions	3 x 3	mm²	Area
Detector A Thickness	65	µm	Shallow probing tests
Detector B Thickness	500	µm	Thermal excitation tests
Nominal Impurity (N)	< 5	ppb	Nitrogen concentration
Nominal Impurity (B)	1	ppb	Boron concentration
Electrode Material	Tungsten (W)	N/A	Sputtering evaporation
Electrode Thickness	200	nm	Metalization layer
Diamond Band Gap	≈5.5	eV	Intrinsic electronic property
Atom Displacement Energy	≈43	eV	Resistance to radiation damage
Average Energy per e/h Pair	13.6	eV	Ionization energy in diamond
Operating Temperature Range	24 to 215	°C	IBIC characterization limit
CCE Drop (RT, Holes)	≈60	%	Polarization effect after 5 min
CCE Drop (175 °C, Holes)	≈13	%	Polarization reduction via heating
IBIC Probing Ions	H⁺, He⁺⁺, C³⁺	N/A	MeV energy ions used
Low Electric Field Tested	±0.18	V/µm	Used to enhance polarization effects

Key Methodologies

The study utilized the Ion Beam Induced Charge (IBIC) technique with a nuclear microprobe to characterize charge transport properties and monitor polarization quenching in sc-CVD diamond detectors.

Material Preparation:
- Electronic grade sc-CVD diamond crystals (65 µm and 500 µm thick) were sourced.
- Front and back surfaces were coated with 200 nm Tungsten (W) electrodes using sputtering evaporation.
- Samples were mounted on ceramic printed circuit boards (PCBs) for high-temperature compatibility.
Irradiation and Probing:
- A 6 MV tandem Van der Graaff accelerator provided focused ion beams (protons, helium, carbon) with MeV energies.
- Focused ion beams (≈1 kcps count rate) were used to induce polarization and probe charge transport from shallow to intermediate depths.
- The IBIC pulses were processed using a standard nuclear spectroscopy electronic chain.
Quenching Techniques Tested:
- Thermal Excitation: A ceramic heater was used to test temperatures from 24 °C (RT) up to 175 °C (below the 200 °C limit imposed by leakage current instability).
- Bias Switching (On/Off): Bias was manually switched on/off during continuous or discontinuous irradiation (50% duty cycle, 30 s intervals).
- Alternating Bias: An in-house HV alternating unit provided periodic rectangular voltage pulses, switching polarity (e.g., +12 V to -12 V) during continuous irradiation.
- Optical Excitation: A standard light source (maximum emission centered around 592 nm) was installed to illuminate the sample during irradiation, primarily targeting damaged regions.
Data Analysis:
- The temporal evolution of CCE was quantified by extracting events in fixed time intervals and fitting Gaussian curves to the pulse height spectra centroids.

6CCVD Solutions & Capabilities

This research confirms the critical role of high-quality, electronic-grade Single Crystal Diamond (SCD) in advanced radiation detection systems, particularly those operating under conditions where polarization quenching is necessary (e.g., high-temperature, high-flux environments). 6CCVD is uniquely positioned to supply the required materials and custom engineering services to replicate and extend this work.

Applicable Materials

To achieve the high spectroscopic performance and low leakage current demonstrated in this study, researchers require the highest purity diamond material.

Electronic Grade Single Crystal Diamond (SCD): 6CCVD offers high-purity SCD plates, essential for minimizing intrinsic defects (traps) that lead to polarization. Our SCD material is ideal for replicating the performance of the detectors (Detector A: 65 µm, Detector B: 500 µm) used in this study.
Boron-Doped Diamond (BDD): For applications requiring specific conductivity or alternative electrode structures, 6CCVD can supply custom Boron-Doped Diamond (BDD) films, which may offer different charge transport characteristics relevant to polarization studies.

Customization Potential

The experimental setup relied on specific dimensions, thicknesses, and electrode materials—all core specialties of 6CCVD.

Requirement from Paper	6CCVD Capability	Sales Advantage
Thickness (65 µm & 500 µm)	SCD and PCD available from 0.1 µm up to 500 µm. Substrates up to 10 mm thick.	Precise control over active detection volume for optimized charge collection and energy deposition studies (e.g., shallow vs. intermediate probing).
Dimensions (3x3 mm² & 1.5x1.5 mm²)	Custom plates/wafers up to 125 mm (PCD). Custom laser cutting for SCD plates.	Supply of custom-sized detectors, including large-area PCD for high-flux tracking or inch-size SCD for advanced array development.
Metalization (200 nm W)	Internal metalization capability including Au, Pt, Pd, Ti, W, and Cu.	We can replicate the Tungsten (W) electrodes used in this study or provide alternative metal stacks (e.g., Ti/Pt/Au) optimized for ohmic contact stability and high-temperature operation (up to 215 °C and beyond).
Surface Quality	SCD polishing to Ra < 1 nm. Inch-size PCD polishing to Ra < 5 nm.	Ensures minimal surface defects that could contribute to surface polarization effects, crucial for high-resolution IBIC mapping.

Engineering Support

The successful implementation of polarization quenching techniques (thermal, optical, and bias cycling) requires deep knowledge of diamond defect physics and detector engineering.

Defect and Trap Analysis: 6CCVD’s in-house PhD team specializes in MPCVD growth parameters and post-processing techniques. We can assist researchers in selecting materials with optimized impurity profiles (< 5 ppb N, 1 ppb B) to minimize intrinsic traps, or intentionally introduce specific dopants for advanced defect engineering.
High-Temperature Applications: Given the finding that heating above 90 °C is highly effective for quenching polarization, 6CCVD provides robust SCD substrates suitable for integration into high-temperature detector assemblies, supporting future studies aiming for temperatures up to 400 °C.
Application Focus: We offer consultation for similar Ion Beam Induced Charge (IBIC) and High Energy Physics projects, ensuring the material properties (purity, thickness, and electrode configuration) are perfectly matched to the required spectroscopic performance and operational environment.

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

View Original Abstract

Synthetic single crystal diamond grown using the chemical vapor deposition technique constitutes an extraordinary candidate material for monitoring radiation in extreme environments. However, under certain conditions, a progressive creation of space charge regions within the crystal can lead to the deterioration of charge collection efficiency. This phenomenon is called polarization and represents one of the major drawbacks associated with using this type of device. In this study, we explore different techniques to mitigate the degradation of signal due to polarization. For this purpose, two different diamond detectors are characterized by the ion beam-induced charge technique using a nuclear microprobe, which utilizes MeV energy ions of different penetration depths to probe charge transport in the detectors. The effect of polarization is analyzed by turning off the bias applied to the detector during continuous or discontinuous irradiation, and also by alternating bias polarity. In addition, the beneficial influence of temperature for reducing the effect of polarization is also observed. Finally, the effect of illuminating the detector with light is also measured. Our experimental results indicate that heating a detector or turning off the bias, and then applying it during continuous irradiation can be used as satisfactory methods for recovering the CCE value close to that of a prepolarized state. In damaged regions, illumination with white light can be used as a standard method to suppress the strength of polarization induced by holes.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma15010388

References

2020 - Test of innovative silicon detectors for the monitoring of a therapeutic proton beam [Crossref]
2021 - Development and characterization of a large area silicon pad array for an electromagnetic calorimeter [Crossref]
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2021 - High-Performance Single-Crystal Diamond Detector for Accurate Pulse Shape Discrimination Based on Self-Organizing Map Neural Networks [Crossref]
2020 - Diamond Detectors for Timing Measurements in High Energy Physics [Crossref]
2021 - Performance of CVD diamond detectors for single ion beam-tagging applications in hadrontherapy monitoring [Crossref]