| 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 |
- Core Focus: BNLâs Instrumentation Department is advancing High-Z semiconductor detectors (CZT, TlBr, CsPbBr3, HPGe, a-Se) across the entire development cycle, from material synthesis to integrated readout electronics.
- VFG Architecture Success: The Position-sensitive Virtual Frisch-Grid (VFG) design, optimized for large-volume bar crystals, achieved exceptional energy resolution: 0.9% FWHM at 662 keV for CZT and 1.6% FWHM for TlBr, utilizing novel 3D position correction techniques.
- Radiation Hardness: CZT VFG detectors demonstrated strong radiation resistance, maintaining performance after proton exposure up to 4 x 107 p/cm2, crucial for Low Earth Orbit (LEO) space missions.
- High-Resolution Spectroscopy: HPGe detectors, utilizing trench segmentation and the MARS ASIC, achieved a high energy resolution of 450 eV FWHM at 60 keV (241Am), essential for high-rate synchrotron X-ray spectroscopy.
- High Spatial Resolution Imaging: Amorphous Selenium (a-Se) detectors, integrated monolithically onto CMOS ASICs (MM-PAD), achieved a spatial resolution (PSF) of approximately 5 ”m, suitable for high-flux, high-energy X-ray imaging.
- Emerging Perovskites: CsPbBr3 is confirmed as a promising candidate, demonstrating a best-reported energy resolution of 1.4% FWHM at 662 keV and high radiation tolerance (up to 1 Mrad).
| Parameter | Value | Unit | Context |
|---|
| CZT Resistivity | ~1 x 1010 | Ω.cm | Room Temperature |
| CZT Mobility-Lifetime (”Ï) | ~5 x 10-3 | cm2/V | Room Temperature |
| CZT VFG Crystal Size | 8 x 8 x 32 | mm3 | Proton Irradiation Test |
| CZT VFG Energy Resolution | 0.9% FWHM | @ 662 keV | 3D corrected spectrum |
| CZT VFG Radiation Tolerance | 4 x 107 | p/cm2 | Protons (100-150 MeV) |
| TlBr Resistivity | ~3 x 1011 | Ω.cm | Room Temperature |
| TlBr VFG Energy Resolution | 1.6% FWHM | @ 662 keV | 3D corrected spectrum |
| TlBr Electron Lifetime | 1.2 | ms | Estimated from drift time |
| HPGe Energy Resolution | 450 | eV FWHM | @ 60 keV (241Am source) |
| HPGe Strip Size | 0.5 x 5 | mm | 64-strip sensor |
| HPGe Readout ASIC | MARS | - | 32 channels, 4 programmable gains (12.5-75 keV) |
| a-Se Bandgap | ~2.1 | eV | Semiconductor material |
| a-Se Dark Current | ~10 | pA/mm2 | Under moderate electric fields |
| a-Se Spatial Resolution (PSF) | ~5 | ”m | Cu Kα radiation, monolithic CMOS integration |
| CsPbBr3 Bandgap | 2.3 | eV | Direct band gap |
| CsPbBr3 Density | 4.85 | g/cm3 | High-Z material |
| CsPbBr3 Highest Resistivity | ~343 | GΩ.cm | Single crystal (Bridgman method) |
| CsPbBr3 Radiation Tolerance | 1 | Mrad | Gamma rays (negligible change in ”Ï) |
| CsPbBr3 BNL Test Resolution | 2.8% FWHM | @ 662 keV | 3D corrected spectrum (3 x 3 x 6 mm3 crystal) |
- Virtual Frisch-Grid (VFG) Detector Design: Utilizes bar-shaped crystals (CZT, TlBr, CsPbBr3) with long drift lengths, maximizing volume while minimizing the number of readout channels. The design achieves electrostatic shielding via specific contact geometries (e.g., grounded electrodes on crystal sides).
- 3D Position Correction: Implemented to overcome non-uniformity in detector response, which is typical for single-type-carrier collection mode materials.
- The technique uses synchronized samples from pad waveforms to estimate X-Y coordinates.
- The Z coordinate (interaction depth) is estimated using the ratio of the cathode signal (C) or sum of pad signals (P) to the anode signal (A), or via carrier drift time.
- This correction significantly improves energy resolution (e.g., from 3.6% raw data to 0.9% FWHM for CZT).
- HPGe Fabrication and Readout:
- Planar Ge detectors fabricated using lithium diffusion (n-type contact) and boron implantation (p-type layer).
- Pixel isolation achieved via trenching, simplifying fabrication compared to traditional methods.
- Readout uses the MARS ASIC, a high-rate front-end system that records real-time photon arrival by logging the system clock value synchronized with the peak-detect signal.
- Amorphous Selenium (a-Se) Monolithic Integration:
- a-Se is deposited directly onto CMOS readout ASICs (MM-PAD) via thermal evaporation at low temperatures.
- This process eliminates the need for complex hybrid bonding, enabling pixel sizes < 10 ”m and high spatial resolution (~5 ”m PSF).
- CsPbBr3 Crystal Growth:
- Various methods explored, including Inverse Temperature Crystallization (ITC) and Electronic Dynamic Gradient (EDG).
- ITC involves decreasing solubility by increasing temperature (75-90 °C range) or using solvent mixtures (e.g., DMSO/CyOH/DMF) to control nucleation sites and grow larger crystals (up to 10 mm per side).
- Purification of precursors (PbBr2 and CsBr) via sublimation or frit filtering is critical to achieving high bulk resistivity (up to 1010 Ω.cm).
- Medical Imaging:
- Computed Tomography (CT) and Single-Photon Emission Computed Tomography (SPECT) systems (CZT).
- Digital Radiography and Mammography (a-Se, high spatial resolution).
- Scientific Research Facilities (Synchrotrons/FELs):
- High-rate X-ray spectroscopy and diffraction (HPGe, MARS ASIC readout).
- X-ray Absorption Fine Structure Spectroscopy (XAFS) (HPGe).
- High dynamic range, high-speed X-ray imaging (a-Se, MM-PAD ASIC).
- Astrophysics and Space Instrumentation:
- All-sky Medium Energy Gamma-ray Observatory (AMEGO) concept (CZT VFG arrays).
- Gamma-ray astronomy and double beta decay searches (CZT, HPGe).
- Security and Nonproliferation:
- Radioisotope Identification Devices (RIID) (TlBr VFG, compact and sensitive).
- Portal security screening (High-Z detectors).
- Industrial Inspection:
- General gamma-ray and hard X-ray inspection systems (CZT, TlBr, CsPbBr3).
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.
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