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

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

Executive Summary

This study investigates various techniques to mitigate polarization—the progressive degradation of Charge Collection Efficiency (CCE) due to space charge accumulation—in synthetic single-crystal Chemical Vapor Deposition (sc-CVD) diamond detectors using Ion Beam Induced Charge (IBIC) microscopy.

Thermal Quenching Efficacy: Heating the detector is a highly effective method for mitigating hole-induced polarization. CCE degradation for holes was reduced from approximately 60% at room temperature (RT) to about 13% at 175 °C. The effect was observed to be largely independent of temperature above 90 °C.
Bias Cycling (Continuous Irradiation): Turning off the bias voltage while the ion beam remains active is a satisfactory method for recovering CCE. The continuous generation of free carriers allows for recombination with trapped space charge, partially restoring the internal electric field.
Bias Cycling (Discontinuous Irradiation): Switching off both the bias and the ion beam simultaneously resulted in minimal CCE recovery. The absence of new free carriers inhibits the necessary recombination process to neutralize the accumulated space charge.
Optical Quenching (Damaged Regions): Illumination with white light (peak emission 592 nm) successfully suppressed hole-induced polarization in radiation-damaged regions by promoting the de-trapping of holes. However, light increased the degradation rate for electron-induced polarization.
Alternating Bias Polarity: Applying periodic alternating bias pulses showed only partial recovery for holes and no significant recovery for electrons. Strong hole polarization quickly resumed upon switching back to positive polarity.
Conclusion for Holes: Heating the detector (greater than 90 °C) or using bias on/off cycling during continuous irradiation are the most reliable methods identified for recovering CCE degraded by hole polarization.

Technical Specifications

Parameter	Value	Unit	Context
Detector Material	sc-CVD Diamond	N/A	Electronic Grade (Element Six)
Detector A Dimensions	3 x 3	mm²	65 µm thickness
Detector B Dimensions	1.5 x 1.5	mm²	500 µm thickness
Impurity Concentration (N)	less than 5	ppb	Nominal
Impurity Concentration (B)	1	ppb	Nominal
Electrodes	Tungsten (W)	200 nm	Sputtering evaporation
Probing Ion Beam (Shallow)	4 MeV C³⁺	N/A	Range ≈2.0 µm in diamond
Probing Ion Beam (Intermediate)	3 MeV He⁺⁺	N/A	Range ≈5.8 µm in diamond
Damaging Ion Beam (DIBs)	5 MeV H⁺	N/A	Traversing beam
Detector A Bias (Low Field)	±12	V	E = ±0.18 V/µm
Detector B Bias (Heated Tests)	±225	V	E = ±0.45 V/µm
Operating Temperature Range	24 to 175	°C	IBIC measurements
Leakage Current (500 µm, 215 °C)	≈100	nA	At 225 V bias
Hole CCE Drop (RT, 5 min)	≈60	%	Continuous irradiation, maximum polarization
Hole CCE Drop (175 °C, 5 min)	≈13	%	Thermal quenching effectiveness
Electron CCE Drop (RT to 175 °C)	≈2	%	Minimal polarization observed
Optical Excitation Wavelength	592	nm	Maximum emission of white light source
Alternating Bias Cycle A (T-/T+)	20/30	s	V_BIAS = ±12 V
Alternating Bias Cycle B (T-/T+)	20/40	s	V_BIAS = ±30 V

Key Methodologies

The study utilized the Ion Beam Induced Charge (IBIC) technique at the Ruđer Bošković Institute (RBI) microprobe to monitor CCE degradation and recovery in real-time.

Detector Preparation and Setup: sc-CVD diamond detectors (65 µm and 500 µm thick) with tungsten electrodes were mounted on ceramic PCBs. A new microprobe setup included a ceramic heater, a high voltage (HV) alternating unit, and a white light source for quenching experiments.
IBIC Characterization: Focused ion beams (4 MeV C³⁺, 3 MeV He⁺⁺) were used as shallow probes to induce charge carriers near the biased electrode, allowing the study of charge transport governed primarily by a single carrier type (holes for positive bias, electrons for negative bias).
Thermal Excitation Protocol: CCE temporal evolution was measured at 24 °C (RT), 95 °C, and 175 °C. The detector was allowed 5 minutes to thermally stabilize before irradiation began. Low electric fields (E < 0.5 V/µm) were used to enhance polarization effects.
Bias On/Off Cycling:
- Continuous Beam: Bias was manually switched on for 30 s and off for 30 s, while the 4 MeV C³⁺ beam continuously irradiated the sample.
- Discontinuous Beam: Bias and beam were simultaneously switched on for 30 s and off for 30 s (using a gate valve to stop the beam).
Alternating Bias Polarity: An HV alternating unit applied periodic rectangular voltage pulses, switching between positive and negative polarities (e.g., 20 s negative, 30 s positive) during continuous 4 MeV C³⁺ irradiation.
Optical Excitation Protocol: The 65 µm detector, including pre-damaged regions (fluences up to 1.7 x 10¹⁴ ions/cm²), was continuously irradiated. CCE was monitored for 300 s in the dark, followed by 180 s with continuous white light illumination (592 nm peak), and then 300 s again in the dark.

Commercial Applications

The findings regarding polarization quenching are critical for ensuring the long-term stability and reliability of sc-CVD diamond detectors in extreme environments, supporting applications in:

High Energy Physics (HEP): Used as tracking detectors and beam monitors (e.g., CERN Large Hadron Collider, SuperKEKB collider) where high radiation fluence causes rapid polarization.
Nuclear Reactors and Fusion Devices (ITER): Diamond detectors are candidates for fast-ion loss detection and neutron monitoring, requiring operation in high-temperature and high-radiation fields.
Medical Dosimetry: Used for radiation therapy monitoring (protons, X-rays), where stable CCE is essential for accurate dose measurement.
Space Applications: Monitoring radiation in outer space environments, benefiting from diamond’s high radiation resistance and low leakage current at high temperatures.
Harsh Environment Monitoring: General radiation monitoring in environments characterized by high temperature (up to 200 °C tested here) and high radiation damage, where silicon detectors fail.

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]
2020 - Measurements with silicon detectors at extreme neutron fluences [Crossref]
1997 - Natural diamond detector as high energy particles spectrometer [Crossref]
2010 - Diamond growth by chemical vapour deposition [Crossref]
2020 - Proton irradiation tests of single crystal diamond detector at CIAE [Crossref]
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]

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

At a Glance