Pulse-height defect in single-crystal CVD diamond detectors

At a Glance

Metadata	Details
Publication Date	2017-02-01
Journal	The European Physical Journal A
Authors	O. Beliuskina, A. O. Strekalovsky, А. А. Александров, И. А. Александрова, H. M. Devaraja
Institutions	GSI Helmholtz Centre for Heavy Ion Research, CEA LIST
Citations	7
Analysis	Full AI Review Included

Technical Documentation and Analysis: Single-Crystal CVD Diamond Detectors for Heavy Ion Spectroscopy

Executive Summary

This study, analyzing the Pulse-Height Defect (PHD) in single-crystal Chemical Vapor Deposition (scCVD) diamond detectors (DD) for low-energy heavy ions, confirms diamond’s superior potential in extreme environment spectroscopy, positioning 6CCVD’s SCD material as the optimal choice for nuclear physics and heavy ion detection systems.

Significant PHD Quantified: Confirmed that PHD is substantial for low-energy heavy ions (20-90 MeV), reaching up to 50% for high-mass ions (e.g., Au), necessitating precise calibration strategies.
Superior Speed Performance: Demonstrated that the calculated plasma time ($\tau_p$) in scCVD diamond ($\sim 1$ ns) is approximately 10 times faster than in silicon (10-20 ns), offering a critical advantage for high-rate Time-of-Flight (ToF) and $\Delta E-E$ telescope systems.
High Field Operation Confirmed: Verified that charge collection efficiency increases significantly with higher electric fields, operating successfully at 2.5 V/µm, leveraging diamond’s intrinsic breakdown strength (up to 10⁷ V/cm).
Calibration Protocol Validation: Successfully adapted standard Silicon detector empirical calibration methods (Schmitt and Moulton) to precisely quantify and correct the PHD in scCVD diamond, providing a practical guide for engineers.
Material Requirement: The results validate the need for high-purity Single Crystal Diamond (SCD) material, confirming the relationship between material characteristics (carrier mobility, defect density) and detector response.

Technical Specifications

The following table summarizes the key material properties and experimental parameters relevant to the scCVD diamond detector operation in heavy ion environments.

Parameter	Diamond Value	Unit	Context
Detector Material	Single-Crystal CVD (scCVD)	N/A	Produced by Element Six
Detector Dimensions	2.7 diameter, 100 thick	mm, µm	Custom size for heavy ion scattering
Electrode Material	Aluminum (Al)	N/A	Schottky contacts
Electrode Thickness	100	nm	Minimal dead layer requirement
Operating Electric Field (Typical)	2	V/µm	Standard condition for heavy ion tests
Electric Field (Max Tested)	2.5	V/µm	Charge collection dependency test
Maximum Applied Voltage (Preamplifier Limit)	250	V	Corresponds to 2.5 V/µm on 100 µm detector
Maximum Breakdown Field (Diamond)	10⁷	V/cm	Intrinsic material limit ($\sim 10\times$ higher than Si)
Energy to create e-h pair ($E_{i}$)	13	eV	Superior ionization efficiency vs. Si (3.6 eV)
Electron Mobility ($\mu_e$)	2200	cm²/Vs	Measured at 300K
Hole Mobility ($\mu_h$)	1600	cm²/Vs	Measured at 300K
Resistivity ($\rho$)	>10¹¹	$\Omega$cm	Required for radiation detection
Plasma Time ($\tau_p$) (Calculated)	$\sim 1$	ns	Key factor for high-speed operation
Maximum PHD Measured	$\sim 50$	%	For heavy ions (Au, Xe) in 20-90 MeV range

Key Methodologies

The Pulse-Height Defect analysis was conducted using a highly controlled nuclear physics setup at the JINR IC-100 cyclotron in Dubna, Russia. The methodology combined advanced scCVD material handling with precise Time-of-Flight (ToF) and energy measurements.

Detector Preparation: A 100 µm thick scCVD diamond wafer (2.7 mm diameter) was metalized on both sides with 100 nm Aluminum layers to create Schottky electrodes.
Ion Beam Generation: A 132Xe beam (130 MeV) was scattered elastically off thin targets (Ti, Cu, Nb, Ag, Au) to produce the specific heavy ions for testing in the 20-90 MeV range.
Energy Modulation (Degrader System): A custom degrader foil (featuring 1 µm and 2 µm Ti strips) was installed to allow simultaneous measurement of three distinct kinetic energy levels ($E_k$) for a single ion species.
Kinetic Energy Measurement ($E_k$): The true kinetic energy ($E_k$) was determined using a Time-of-Flight (ToF) system, calibrated using $\alpha$ particles from a $^{226}$Ra source.
Deposited Energy Measurement ($E_{DD}$): The diamond detector measured the resulting pulse height (apparent energy). The PHD ($\Delta E = E_k - E_{DD}$) was calculated from the difference.
Electric Field Study: Fission fragments of $^{252}$Cf were utilized to investigate the dependence of charge collection efficiency (and thus PHD) on the applied electric field, ranging from 0.7 V/µm up to 2.5 V/µm.
Modeling and Calibration: Experimental data were fitted using modified recombination models (Akimov et al.) and two Si-detector empirical calibration methods (Schmitt et al. and Moulton et al.) to establish reliable PHD calibration curves for DDs.

6CCVD Solutions & Capabilities

6CCVD provides the necessary specialized materials and fabrication expertise to replicate, extend, and optimize the high-performance diamond detectors described in this research. Our capabilities directly address the strict material purity, dimensional control, and metalization requirements of advanced heavy-ion spectroscopy.

Component Requirement from Research Paper	6CCVD Solution & Capability	Competitive Advantage
Required Material Purity	Optical Grade Single Crystal Diamond (SCD)	SCD is mandatory to achieve the high carrier mobility (2200 cm²/Vs) and low defect density required to minimize residual recombination losses ($\Delta E_r$) and subsequent PHD.
Detector Dimensions	Custom Thin Wafers and Precision Cutting	The tested detector (2.7 mm diameter, 100 µm thick) fits perfectly within our core offerings. 6CCVD supplies SCD wafers in thicknesses from 0.1 µm to 500 µm and provides custom laser cutting for precise circular or complex shapes up to large-area dimensions (up to 125 mm diagonal for PCD).
Electrode Fabrication	Advanced Metalization Services	We offer internal deposition of the necessary Schottky contacts. While Al (100 nm) was used here, 6CCVD provides high-reliability, multi-layer metalization stacks including Ti, Pt, Au, Pd, W, and Cu, optimized for bonding, low contact resistance, and entrance window minimization ($\Delta E_w$).
Surface Quality	Ultra-Smooth Polishing (Ra < 1 nm)	Achieving superior surface finish (Ra < 1 nm for SCD) is critical, as surface recombination affects PHD. Our advanced polishing minimizes surface traps, improving charge collection completeness.
Engineering Parameters	High-Voltage Reliability	Our SCD materials are guaranteed to possess the intrinsic properties necessary to withstand the high electric fields (approaching the 10⁷ V/cm breakdown limit) required for charge collection saturation in dense plasma tracks.

Material Recommendations for Heavy Ion Detectors

To exceed the performance outlined in the research, 6CCVD recommends the following specific material configuration:

Material: High-purity Optical Grade Single Crystal Diamond (SCD).
Thickness Range: 50 µm to 300 µm (Optimized for specific heavy ion stopping ranges and $\Delta E$ applications).
Polishing: Standard Ra < 1 nm (essential for spectroscopic applications).
Metalization: Custom multi-layer Ti/Pt/Au for optimal ohmic/Schottky contacts and wire bonding compatibility, ensuring long-term operational stability under heavy radiation.

Engineering Support

The analysis of the Pulse-Height Defect relies heavily on sophisticated models incorporating plasma time ($\tau_p$), energy deposition profiles (SRIM), and empirical fitting functions (Equations 16-19). 6CCVD’s in-house PhD material science and engineering team is available to assist researchers in:

Selecting the optimal SCD material purity and thickness tailored to specific heavy-ion energies (20-100 MeV range).
Designing and implementing detector stacks, including custom metalization layers, to minimize dead layers ($\Delta E_w$) and maximize signal fidelity.
Consulting on material parameters (like mobility and lifetime) to refine and validate recombination models for next-generation $\Delta E-E-ToF$ systems.

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

Tech Support

Original Source

DOI: https://doi.org/10.1140/epja/i2017-12223-8