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TiBr, SiC and Amorphous Seiconductor

Session chair: Mandal , Krishna C. (University of South Carolina, Electrical Engineering, Columbia, USA); Fraboni , Beatrice (University of Bologna, Department of Physics and Astronomy, Bologna, Italy)
Shortcut: R-06
Date: Wednesday, 20 October, 2021, 9:15 AM - 11:15 AM
Room: RTSD
Session type: RTSD Session


Click on an contribution to preview the abstract content.

9:15 AM R-06-01

Optimization of TlBrCl Crystal for Cherenkov Photon Time Resolution (#1010)

C. Kim1, K. Shimazoe1, H. Takahashi1, K. Hitomi2, M. Nogami2

1 The University of Tokyo, Department of Bioengineering, Bunkyo, Japan
2 Tohoku University, Department of Quantum Science and Energy Engineering, Aoba, Japan


The optical performance of thallium bromide chloride (TlBrXClX-1) was evaluated in terms of the detection rate and coincidence time resolution (CTR) by detecting Cherenkov photons. Radiation detectors were fabricated by coupling TlBr and TlBrXClX-1 crystals with dimensions of 3 × 3 × 3 mm3 to a SiPM. The addition of thallium chloride (Cl) to thallium bromide (TlBr) improves the detection rate by a factor of 3, and the best CTR of 319 ± 6.8 ps and 329 ± 3.2 ps width half maximum (FWHM) were obtained from TlBr and TlBrXClX-1 detectors, respectively. The proper crystal surface treatment, an unpolished surface in this experiment, significantly improves the timing performance, and the obtained CTR was 264 ± 2.6 ps FWHM. The results demonstrated that the optical performance of TlBr can be improved by mixing TlCl, and TlBrXClX-1 is a promising candidate material for radiation detectors that require an excellent energy resolution and time resolution.

Keywords: thallium bromide, thallium chloride, Cherenkov photon, semiconductor radiation detectors
9:30 AM R-06-02

Analysis of Position-Sensitive Capacitive Frisch-Grid TlBr Detectors (#133)

A. Kargar1, A. Bolotnikov3, C. A. Brown1, G. Carini3, M. Smith2, J. Christian1, L. Cirignano1, A. Dellapenna3, G. Deptuch3, J. Fried3, S. Herrmann3, H. Kim1, G. Pinaroli3, M. Koslowsky2, A. Valente2, S. Miryala3, C.-R. Deane3, A. Miller2, K. Shah3, M. Squillante1, E. Raguzin3, M. Squillante1, E. Weststrate1, K. Shah1

1 Radiation Monitoring Devices (RMD) Inc., Watertown, Massachusetts, United States of America
2 Bubble Technology Industries (BTI) Inc., Chalk River, Ontario, Canada
3 Brookhaven National Laboratory (BNL), Upton, New York, United States of America


This work presents results from analyzing position-sensitive capacitive Frisch-grid (PS-CFG) TlBr gamma-ray detectors. As a room-temperature semiconductor detector, TlBr exhibits a high atomic number, high density, and low Fano factor compared to other material.  The use of the 3-D position sensing technique provides information on the crystal uniformity.  This technique presents the spatial variation in the histograms of the anode amplitude versus the cathode-to-anode ratio, necessary for depth correction, for detectors fabricated with 5×5×12 mm3 TlBr crystals at room temperature operating at continuous bias (1.5 kV) over the course of nine months.  This work also presents the temperature dependence of the leakage current for a TlBr PS-CFG detector over the temperature range of -20 to +60 °C, which varies from <0.2 to 40 nA, respectively, along with changes in the spectrum from the anode signal measured with 137Cs irradiation.  This work shows the utility of the 3-D technique to evaluate the performance and uniformity of PS-CFG detectors for applications that require high-energy resolution gamma-ray spectroscopy, such as radionuclide identification.


Summary received April 5, 2021. This work has been supported by the U.S. Department of Homeland Security, Countering Weapons of Mass Destruction Office, under competitively awarded contract 70RDND18C00000024. This support does not constitute an express or implied endorsement on the part of the Government.

Keywords: TlBr semiconductor, Position-sensitive Capacitive Frisch-Grid, Room-temperature gamma-ray detector.
9:45 AM R-06-03

Characterization of long-term stability of thallium bromide gamma-ray detectors (#862)

K. Hitomi1, M. Nogami1, T. Onodera2, K. Watanabe3, K. Ishii1

1 Tohoku University, Sendai, Japan
2 Tohoku Institute of Technology, Sendai, Japan
3 Kyushu University, Fukuoka, Japan


Thallium bromide (TlBr) gamma-ray detectors exhibit very high photon stopping power and excellent energy resolutions at room temperature. However, widespread use of the detectors has been limited mainly due to the instability of the performance at room temperature. Long-term stability of TlBr detectors was characterized in this study. TlBr crystals were grown by the traveling molten zone method using zone-purified materials. Gamma-ray detectors were fabricated by constructing Tl-based metal electrodes on the crystals. A 2-mm-thick TlBr detector with a planar cathode and a pixelated anode (1.5 mm × 1.5 mm) surrounded by a guard electrode was irradiated with a 137Cs gamma-ray source at room temperature.  A bias voltage of -200 V was applied to the cathode. The pixelated anode and the guard electrode were maintained at the ground potential. The detector was operated for more than 2000 hours. The pulse height spectra and the leakage currents were monitored during the operation. The detector exhibited stable spectroscopic performance at room temperature. The peak position for 662-keV gamma rays decreased approximately 5% during the measurement.

Keywords: Gamma-ray detectors, compound semiconductor, thallium bromide, TlBr, long-term stability
10:00 AM R-06-04

Low Energy γ-Detection with 250 µm Ni/n-4H-SiC Epitaxial Schottky Barrier Diode (#998)

J. W. Kleppinger1, S. K. Chaudhuri1, K. C. Mandal1

1 University of South Carolina, Department of Electrical Engineering, Columbia, South Carolina, United States of America


A high-resolution Schottky barrier detector has been fabricated in our laboratory using a 250 µm thick 4H-SiC epilayer. Capacitance-voltage (C-V) measurements on the detector revealed a low effective carrier concentration of ~6 x 1013 cm-3 allowing the epilayer to be fully depleted at a bias as low as 3 kV.  Furthermore, the leakage current remained below 100 pA up to 790 V. The radiation detection performance was evaluated from the pulse height spectra of an alpha (5486 keV) and gamma (59.54 keV) emitting 0.9 µCi 241Am radiation source. Due to the low effective carrier concentration, the alpha pulse height spectrum saturated as early as 20 V and displayed a resolution of 0.47 % FWHM. The gamma peak was observed at a resolution of 13.5% at 710V applied reverse bias. Defect levels in the epilayer were characterized by deep level transient spectroscopy (DLTS) which showed the presence of three deep levels, Ti(c), Z1/2, and EH6/7. The microscopic nature of the defects was investigated theoretically by density functional theory (DFT) calculations on intrinsic defects with hybrid density functional and the extended FNV correction. The results show good agreement with levels extracted from the experimental DLTS spectrum.

AcknowledgmentThe authors acknowledge partial financial support from the DOE Office of Nuclear Energy’s Nuclear Energy University Programs (NEUP), Grant No. DE-NE0008662.
Keywords: 4H-SiC, Epitaxial layers, Radiation detectors, DFT calculations, Deep level transient spectroscopy (DLTS).
10:15 AM R-06-05

Charge Transport in 4H–SiC Radiation Detectors with different metallization. (#869)

P. Praus1, E. Belas1, R. Grill1, M. Betusiak1, J. Pipek1, M. Brynza1, J. Kunc1

1 Charles University, Institute of Physics, Prague, Czech Republic


Characterization of transport and spectroscopic properties of 4H–SiC radiation detectors prepared with different types of metal (Au/Au, AuCr/AuCr, Cr/Cr, Ni/Ni) and graphene/graphene (G/G) semi-transparent electrical contacts will be presented. Laser–induced Transient Current Technique (L–TCT) and other standard characterization methods such as alpha spectroscopy and I-V characteristics measurement were used for finding optimal preparation method of the detector with the highest mobility–lifetime (µτ) product and low polarization. We observe oscillations of the current transients, where no transit time can be identified. We expand the knowledge about the polarization of the 4H–SiC detector. We estimated the µτ product without taking into account surface recombination. We found that µτ measured at pulsed bias is not affected by the type of metallization and reaches the value of approximately 2.8×10-6 cm2/V. We also found that 4H–SiC detectors quickly polarize applying DC bias with any used contacts. The polarization rate strongly depends on the type of metallization. We found that 4H–SiC detectors with symmetrical Cr/Cr contacts exhibit stable collected charge for the longest time (~100 s). On the other hand, the collected charge for Ni/Ni contact starts to drop after 0.3 s only. The polarization dynamics of detectors with G/G contacts differ from the metal contacts, probably due to the lower graphene conductivity. Full depolarization of the detector with time–stable charge collection is possible by using laser pulse delay (LPD) < 300 µs with a depolarization time of > 100 ms for any used contact. For short LPD we can observe a slight increase in collected charge which drops sharply after reaching the maximum. The initial increase and subsequent sharp decrease of the collected charge are qualitatively well described by the theoretical model.


Financial support from the Grant Agency of the Czech Republic 18-12449S is gratefully acknowledged

Keywords: Silicone carbide, charge trnasport, electrical contacts, transient current technique
10:30 AM R-06-06

High-Resolution Alpha Spectrometry with Epitaxial n-4H-SiC/SiO2 Metal-Oxide-Semiconductor Vertical Radiation Detectors (#987)

O. Karadavut1, J. W. Kleppinger1, S. K. Chaudhuri1, K. C. Mandal1

1 University of South Carolina, Department of Electrical Engineering, Columbia, South Carolina, United States of America


We report the fabrication of MOS capacitors on 4H-SiC for alpha particle detection with the highest energy resolution ever reported. Epitaxially grown SiC, in its 4H polytype, is the perfect choice for harsh environment radiation detection due to its ultra-wide bandgap, high average displacement threshold energy, insensitivity to high temperatures, and excellent charge transport properties. While thin 4H-SiC epitaxial layers offer excellent crystalline quality, exhibit superior charge transport properties, and low operating bias for full depletion, the overall device capacitance generally turns out to be rather high. High device capacitance contributes to the total input capacitance (parallel combination) as seen by the pre-amplifier and increases the overall electronic noise of the spectrometer by elevating the white series and pink noise components. An insulating oxide layer of optimum thickness grown on the 4H-SiC epilayer decreases the device capacitance as the oxide layer capacitance contributes as a series combination to the epilayer capacitance. MOS capacitors were fabricated by growing 100 nm SiO2 layer through dry oxidation on 20 μm thick n-type epitaxial layers. Current-voltage and capacitance-voltage characteristics confirmed the formation of the oxide layer. Radiation detection was carried out using a 0.9 μCi 241Am alpha source emitting primarily 5486, 5443, and 5388 keV alpha particles and a standard analog alpha spectrometer coupled to the detector through an Amptek A250CF CoolFET preamplifier. The detector exhibited an energy resolution of 0.42% for the 5486 keV alpha particles. Detailed noise analysis and capacitance DLTS studies will be presented to investigate the effect of the oxide layer on the detector performance by comparing the MOS detector with that of surface barrier detectors.

AcknowledgmentThe authors acknowledge partial financial support from the DOE Office of Nuclear Energy’s Nuclear Energy University Programs (NEUP), Grant No. DE-NE0008662.
Keywords: 4H-SiC epitaxial layer, radiation detection, metal-oxide-semiconductor (MOS) capacitor, deep level transient spectroscopy (DLTS)
10:45 AM R-06-07

Characterisation of Thick Monolithic Hydrogenated Amorphous Silicon for X-ray Dosimetry (#56)

M. J. Large1, M. Bizzarri2, 3, M. Boscardin5, 4, L. Calcagnile2, 6, M. Capri2, A. Caricato2, 6, P. Cirrone2, 7, M. Crivellari5, I. Cupparo2, 8, G. Cuttone2, 7, J. Davis1, S. Dunand2, 9, L. Fano2, 3, O. Hammad Ali5, M. Ionica2, K. Kanxheri2, G. Maruccio2, 6, M. Menichelli2, A. G. Monteduro6, A. Morozzi2, 11, F. Moscatelli2, 10, A. Papi2, D. Passeri2, 11, M. Petasecca1, G. Quarta2, 6, S. Rizzato2, 6, A. Rossi2, 3, G. Rossi2, A. Scorzoni2, 11, L. Servoli2, C. Talamonti2, 8, G. Verzellesi2, 4, N. Wyrsch9

1 University of Wollongong, Centre for Medical Radiation Physics, Wollongong, Australia
2 INFN, Perugia, Italy
3 Università degli Studi di Perugia, Dipartimento di Fisica e Geologia, Perugia, Italy
4 INFN Trento, Trento, Italy
5 Fondazione Bruno Keller, Trento, Italy
6 Università di Lecce, Dipartimento di Fisica e Matematica, Lecce, Italy
7 INFN Catania, Catania, Italy
8 Università di Firenze, Dipartimento di Fisica e Astronomia, Fiorentino, Italy
9 Ecole Polytechnique Federale de Lausanne, Institute of Microengineering, Neuchatel, Switzerland
10 CNR-IOM, Perugia, Italy
11 Università degli studi di Perugia, Dipartimento Di Ingegneria, Perugia, Italy

On behalf of the 3D-SiAm Collaboration


In this study, a series of ionizing radiation detectors utilising hydrogenated amorphous silicon (a-Si:H) technologies are characterized for applications in X-ray dosimetry. The fabricated series of detectors consist of a p-i-n diode structure with differing combinations of active area (2x2 and 5x5 mm2) and intrinsic a-Si:H layer thickness (5, 7.3 and 10 µm).  The desirability of a-Si:H arises due to its reliable, reproducible deposition over large areas at low cost compared to crystalline silicon. Furthermore, its demonstrated high radiation hardness and ability to be deposited onto a wide range of substrates (including flexible materials such as Kapton) make this technology an interesting candidate for X-ray dosimetry.  The detectors are characterised via exposure to high energy (6 MV) photons produced from a clinical linear accelerator at reference conditions. The response of all detectors for delivered doses between 25 and 300 cGy was observed to be linear, with regression coefficients ranging from R2 =0.9993 to 1 across the unique detector architectures. Under passive operation of the detectors, the sensitivities of each detector to 6 MV photons were inferred directly from the resulting linearity. An architecture consisting of a 10µm intrinsic a-Si:H layer and 5x5 mm2 active area produced the largest calculated sensitivity of (50.63 +- 0.50) pC/cGy. The dose-rate dependence is also reported for 10µm thick detectors by varying the source-to-surface distance between 80-300 cm and measuring the normalised response against an ionisation chamber Results displayed clear dose rate dependence, with an overresponse by a factor of 2.2 at low dose rates and stabilising for higher rates. Preliminary data suggests operating the devices under reverse bias instead of at 0V may assist in reducing this low dose rate overresponse. Full analysis of results and an evaluation of the a-Si:H detectors will be presented at NSS MIC 2021.

Keywords: Radiation detection, Dosimetry, Amorphous, Radiation damage
11:00 AM R-06-08

The X-ray Sensitivity of Amorphous Lead Oxide Direct Conversion X-ray Detector (#136)

O. Grynko1, T. Thibault2, E. Pineau2, G. DeCrescenzo2, A. Reznik2, 3

1 Lakehead University, Chemistry and Materials Science program, Thunder Bay, Ontario, Canada
2 Lakehead University, Physics Department, Thunder Bay, Ontario, Canada
3 Thunder Bay Regional Health Research Institute, Thunder Bay, Ontario, Canada


Current state-of-the-art direct conversion digital X-ray medical imaging detectors utilize an amorphous Selenium (a-Se) photoconductor as an X-ray–to–charge converter. a-Se–based detectors are successfully used with low-energy X-rays. However, X-ray absorption of a-Se is not strong enough for higher-energy application in diagnostic imaging, which limits the widespread use of the direct conversion scheme to mammography only. Amorphous Lead Oxide (a-PbO) is proposed as an alternative photoconductor to be used in high-energy applications such as radiography or fluoroscopy. It has high X-ray stopping power, low charge creation energy, and a fast temporal response. Previously we have developed a practical approach for the dark current reduction to an acceptably low level at high electric fields while preserving the temporal performance suitable for real-time imaging. It was achieved by the engineering of a blocking layer structure with a polyimide (PI) layer. Here we report on continuing progress in the a-PbO technology by investigating the detector’s X-ray sensitivity, measured as charge creation energy W± – one of the most important parameters of the X-ray detector. The sensitivity of the PI/a-PbO detector was examined in a wide range of experimental parameters, such as electric field, X-ray photon energy and exposure. We demonstrate that W± rapidly decreases with the application of a stronger electric field and saturates at 18–31 eV/ehp, depending on the energy of X-rays, where higher photon energy results in a lower W± (higher sensitivity). On the other side, W± degrades at high exposures, especially at low electric fields. A mechanism responsible for this behaviour is proposed. These findings demonstrate that an a-PbO–based detector performs best at high fields, high X-ray energy, and low exposure, which ideally suits its purpose of low-dose diagnostic X-ray imaging.

AcknowledgmentFinancial support from Teledyne DALSA, NSERC and Mitacs is gratefully acknowledged.
Keywords: Lead Oxide, X-ray digital detector, direct conversion, X-ray sensitivity, columnar recombination

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