Advances in High-Z semiconductor radiation detectors at BNL

At a Glance

Metadata	Details
Publication Date	2025-09-04
Journal	Frontiers in Detector Science and Technology
Authors	G. Pinaroli, A. E. Bolotnikov, M. Bouckicha, F. Capocasa, L. Cultrera
Analysis	Full AI Review Included

Technical Documentation & Analysis: Advances in High-Z Semiconductor Radiation Detectors

This document analyzes the research presented on high-Z semiconductor radiation detectors developed at Brookhaven National Laboratory (BNL) and connects the material requirements and technical challenges to the advanced capabilities offered by 6CCVD’s MPCVD diamond products.

Executive Summary

Core Research Focus: BNL is advancing high-Z semiconductor detectors (CZT, TlBr, CsPbBr₃, Ge, a-Se) for hard X-ray and gamma-ray detection, crucial for astrophysics, medical imaging, and nuclear security (MeV range).
Key Architectural Achievement: The Virtual Frisch-Grid (VFG) architecture, coupled with 3D position correction techniques, dramatically improved energy resolution in CZT detectors from 3.6% (raw) to 0.9% FWHM at 662 keV.
Material Performance: High-Purity Germanium (HPGe) achieved excellent spectroscopic resolution (450 eV FWHM at 60 keV). Amorphous Selenium (a-Se) demonstrated high spatial resolution imaging (5 µm PSF) via monolithic integration with CMOS ASICs.
Emerging Materials: CsPbBr₃ perovskite is highlighted as a promising, low-cost, room-temperature alternative, achieving 1.4% energy resolution at 662 keV, approaching CZT performance.
High-Flux Limitation: High-Z materials like CZT VFG detectors are limited by electronic noise, primarily related to high leakage current (3-5 nA) and large capacitance.
6CCVD Value Proposition: The paper explicitly notes diamond’s excellent charge transport and radiation hardness. 6CCVD’s MPCVD Single Crystal Diamond (SCD) offers a superior low-Z alternative for high-flux, high-rate, and charged particle applications, mitigating the noise and leakage issues inherent in high-Z materials.

Technical Specifications

The following hard data points were extracted from the analysis of high-Z semiconductor detector performance at room temperature (unless otherwise noted):

Parameter	Value	Unit	Context
CZT Resistivity	~1 x 10¹⁰	Ω.cm	Room Temperature
CZT Electron Mobility (µ_e)	1,000	cm²/V.s	Room Temperature
TlBr Resistivity	~3 x 10¹¹	Ω.cm	Room Temperature
CsPbBr₃ Resistivity	10⁹ - 10¹⁰	Ω.cm	High-quality single crystals
CZT VFG Raw Resolution (662 keV)	3.6	% FWHM	Before correction (10x10x32 mm³)
CZT VFG 3D Corrected Resolution (662 keV)	0.9	% FWHM	After 3D correction, 2,200 V bias
TlBr VFG 3D Corrected Resolution (662 keV)	1.6	% FWHM	1.8 kV bias
CsPbBr₃ 3D Corrected Resolution (662 keV)	2.8	% FWHM	3 x 3 x 6 mm³ device
Ge Detector Resolution (60 keV)	450	eV FWHM	²⁴¹Am source, 80 K operation
a-Se Spatial Resolution (PSF)	5	µm	Cu Kα radiation, high-resolution imaging
CZT Proton Radiation Dose Tested	4 x 10⁷	p/cm²	5-year Low Earth Orbit simulation
CsPbBr₃ Gamma Radiation Dose Tested	1	Mrad	Negligible change in resolution/µτ

Key Methodologies

The research utilized advanced material processing and detector architectures to achieve high performance in hard X-ray and gamma-ray detection:

Virtual Frisch-Grid (VFG) Architecture: Employed in CZT, TlBr, and CsPbBr₃ bar-shaped crystals to maximize performance in single-type-carrier collection mode. The VFG design uses grounded electrodes on the crystal sides to achieve electrostatic shielding, minimizing signal dependence on the interaction site location.
3D Position Correction: Achieved by incorporating charge-sensing pads (pixelated anodes) and utilizing the carrier drift time to estimate the Z-coordinate. This technique corrects for response inhomogeneity throughout the detector volume, leading to significant spectral resolution improvement.
Germanium Detector Fabrication: Planar Ge detectors were fabricated using lithium diffusion (n-type contact) and boron implantation (p-type layer). Trench segmentation was used for pixel isolation, simplifying fabrication compared to traditional methods.
Custom Readout Electronics: Detector systems utilized specialized ASICs, including the MARS (Multi-element Amplifier and Readout System) for Ge spectroscopy and the MM-PAD (Mixed-Mode Pixel Array Detector) for a-Se imaging.
Amorphous Selenium (a-Se) Monolithic Integration: a-Se was directly deposited onto CMOS readout ASICs via thermal evaporation at low temperatures, eliminating the need for complex hybrid bonding and enabling high spatial resolution (pixel sizes < 10 µm).
CsPbBr₃ Crystal Synthesis: High-quality single crystals were grown using methods like Bridgman and Inverse Temperature Crystallization (ITC). Purification of precursors (e.g., sublimation, frit filtering) was critical to achieving high bulk resistivity and improved carrier transport properties.

6CCVD Solutions & Capabilities

The BNL research highlights the critical need for materials with excellent charge transport, high radiation tolerance, and precise geometric control for next-generation detectors. While the paper focuses on High-Z materials for MeV detection, 6CCVD’s MPCVD diamond offers superior performance in high-flux, high-rate, and charged particle environments where the electronic noise and leakage current of CZT/TlBr become limiting factors.

Applicable Materials

Application Requirement	6CCVD Material Recommendation	Rationale
High-Flux X-ray/Charged Particle Detection (Where Ge/CZT noise is limiting)	Single Crystal Diamond (SCD)	SCD possesses the highest radiation hardness and superior charge transport properties, ensuring fast response times and minimal signal degradation in high-rate synchrotron or particle physics experiments.
Large-Area, Cost-Effective Arrays (Scaling up detector area)	Polycrystalline Diamond (PCD)	PCD offers a scalable, cost-effective platform for large-area detectors, suitable for industrial inspection or security screening applications requiring robust, radiation-hard sensors.
High-Resolution Spectroscopy (Alternative to HPGe at room temperature)	Boron-Doped Diamond (BDD)	BDD films can be tailored for electrochemical or UV detection applications, leveraging diamond’s stability and wide bandgap, offering room-temperature operation where Ge requires cooling.

Customization Potential

The development of VFG detectors, segmented Ge strips, and pixelated a-Se arrays requires highly customized material dimensions and electrode patterning. 6CCVD is uniquely positioned to supply the foundational diamond materials for similar advanced detector architectures:

Custom Dimensions: We supply SCD and PCD plates/wafers in custom sizes, including large-area PCD up to 125 mm in diameter, enabling the fabrication of scalable, large-volume detector arrays similar to those proposed for CZT.
Thickness Control: We offer precise thickness control for SCD and PCD layers from 0.1 µm up to 500 µm, and robust diamond substrates up to 10 mm thick, suitable for integration into complex detector modules.
Advanced Metalization: The paper discusses complex electrode materials (Yttrium, Pt, Au). 6CCVD offers in-house metalization services, including the deposition of Au, Pt, Pd, Ti, W, and Cu, allowing researchers to design and test custom electrode geometries and blocking contacts directly on diamond surfaces.
Ultra-Smooth Polishing: For high-resolution lithography required for pixelation (like the 5 µm PSF achieved by a-Se), our SCD wafers are polished to an industry-leading surface roughness of Ra < 1 nm. Inch-size PCD wafers achieve Ra < 5 nm.

Engineering Support

6CCVD’s in-house PhD team specializes in the physics and engineering of MPCVD diamond detectors. We can assist researchers and engineers with material selection, device design, and integration challenges for projects requiring:

High-Flux X-ray Beam Monitoring: Utilizing SCD’s extreme radiation hardness and fast response time.
Charged Particle Detection: Leveraging diamond’s low atomic number (low-Z) for minimal scattering and high signal-to-noise ratio.
Custom ASIC Integration: Providing diamond wafers with precise dimensions and metal contacts optimized for bonding to advanced readout electronics (e.g., MARS or MM-PAD ASICs).

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

View Original Abstract

Semiconductor radiation detectors play a crucial role in scientific research and technological applications, with materials typically categorized as low- or high-Z depending on their atomic numbers and densities. This distinction is not strictly defined because the selection of materials depends on the specific application and the energy range. Low-Z semiconductors such as diamond, silicon (Si), selenium (Se), and silicon carbide (SiC) are widely used in X-ray and charged particle detection due to their excellent charge transport properties and radiation hardness. High-Z semiconductors, including germanium (Ge) and compound materials such as cadmium telluride (CdTe), cadmium zinc telluride (CdZnTe or CZT), and emerging lead halide perovskites (most promising is CsPbBr3), offer absorption efficiency in the hard X-ray and gamma-ray regions comparable to CZT. These materials enable advancements in diverse fields, including biology, astrophysics, medical imaging, and industrial inspection. At Brookhaven National Laboratory (BNL), the Instrumentation Department is at the forefront of developing cutting-edge semiconductor detector technologies to address the evolving needs of fundamental and applied research. The projects cover the entire development cycle, from the investigation of new materials and optimization of detector architectures to the design of low-noise readout electronics and signal processing techniques. The ongoing research projects focus on next-generation detection systems that improve sensitivity, energy resolution, and robustness for a wide range of applications. The continuous demand for versatile and high-performance detector systems drives research in multiple directions with emphasis on advancing detector integration within complex experimental requirements, ensuring seamless compatibility with large-scale scientific facilities, and developing scalable and cost-effective fabrication techniques. The combination of novel materials, innovative detector designs, and state-of-the-art readout electronics paves the way for next-generation semiconductor detectors with unprecedented performance. In this work, we present an overview of our recent advances in semiconductor detectors and their applications.

Tech Support

Original Source

DOI: https://doi.org/10.3389/fdest.2025.1630014

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