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Space-Charge Effects and Detector Polarization

Session chair: Procz , Simon (Albert-Ludwigs-Universität Freiburg, FMF - Freiburg Materials Research Center, Freiburg, Germany); Chen , Henry
Shortcut: R-10
Date: Friday, 22 October, 2021, 7:00 AM - 8:45 AM
Room: RTSD
Session type: RTSD Session


Click on an contribution to preview the abstract content.

7:00 AM R-10-01

Investigation of low Earth orbit influence on CdTe and CdZnTe semiconductor detectors with 200MeV proton irradiation (#754)

Y. Uchida1, H. Takahashi1, H. Matake1, R. Imazawa1, K. Sueoka1, T. Mizuno1, Y. Fukazawa1

1 Hiroshima University, Department of Physics, Hiroshima, Japan


We report the radiation damage by 200 MeV proton to Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CdZnTe) semiconductor detectors for MeV gamma-ray observation with Cubesat. The purpose of the experiment is to imitate a low-Earth orbit where there are a lot of cosmic-ray and/or albedo particles. We prepare the two kinds of semiconductor detectors; CdTe is the In Schottky diode type and CdZnTe is the ohmic contact type. After CdTe and CdZnTe are irradiated to 1 krad proton, their background levels are increased by their own radio activation. Most of the radio-activated compounds have a shorter half-life time of less than 1 day. Therefore, the background levels both of CdTe and CdZnTe are reduced by at least 1 digit over time. On the other hand, their energy resolutions are getting worse for the damage of proton, and their gains become lower.


This work was supported by KAKENHI Grant-in-Aid for Young Scientists 21K13946.

Keywords: CdTe, CdZnTe, Low earth orbit satellites, Semiconductor radiation detectors
7:15 AM R-10-02

GPU-Accelerated CZT Detector Simulation with Charge Build-up Effects (#344)

A. Delcourt1, G. Montémont1

1 CEA, Leti, Grenoble, France


The simulation of semiconductor detectors is a key tool in the development or study of this type of device. Most of the time, simulations of CZT detectors assume the crystal to be perfect, meaning that its properties are uniform. However, structural defects appearing in the crystal during growth modify the properties. Moreover, dynamic phenomena like polarisation can appear. In particular, the electric field inside the detector can be disturbed by bulk charges, generating uncertainty on measurement of incident photon energy and on its position estimated by sub-pixel positioning.
One of the main issues of a simulation considering these non-uniformities is its complexity, especially if several electric field distributions have to be considered. Hence, we have developed a model accepting electric field modifications and allowing to observe quickly the detector’s response modifications with the electric field. We leveraged GPU to address such computational burden. Indeed, we can afford to consider more complex simulations as the computation time is reduced.
In this study, we introduced different types of spatial defects which are present in real CZT crystals (punctual, linear, etc.) and to observe quickly and easily their impact on the detector’s measurement, on both spatial and spectral response.

AcknowledgmentThe authors would like to thank Roland Hildebrand from Laboratoire Jean Kuntzmann for his support and the fruitful discussions.
Keywords: CZT Detectors, Detector Simulation, GPU, Material defects, Pixel Detectors
7:30 AM R-10-03

Polarization Effects in CsPbBr3 Radiation Detectors (#985)

R. Toufanian1, A. Datta1, S. Swain1, P. Becla1, S. Motakef1

1 CapeSym, Inc., R&D, Natick, Massachusetts, United States of America


The high mobility, long carrier lifetime, and high absorption coefficient of halide perovskites have rendered them ideal materials for radiation detection. Over the past decade, lead halide perovskites have attracted extensive attention for a myriad of applications, such as photovoltaics, light emitting diodes (LEDs), laser devices, in addition to radiation detection. Here, we report the effect of ion migration on radiation detection properties of CsPbBr3 Schottky-type detectors, and the underlying causes hindering their stable response to gamma radiation. We gain insight into the influence of ion migration on the charge transport properties and energy spectra in these devices and investigate the formation energies and charge transition levels of intrinsic point defects in CsPbBr3, revealing excellent agreement between the theoretical and experimental understanding of defect tolerance in CsPbBr3 detectors.


This material is based upon work supported by the U.S. Department of Energy, Office of DNN R&D Award Number DE-SC0020900.

Keywords: radiation detection, Halide perovskites, Gamma Detector, Defect
7:45 AM R-10-04

High-temperature Effect on Electrical Properties of Cs2AgBiBr6 Radiation Detector Materials (#1035)

G. Yang1, D. Cao1, R. B. James2

1 North Carolina State University, Department of Nuclear Engineering, Raleigh, North Carolina, United States of America
2 Savannah River National Laboratory, Aiken, South Carolina, United States of America


This work aims to study and evaluate the high-temperature electrical performance of solution-grown Cs2AgBiBr6 double perovskite crystals with a Bi-poor precursor. Such a new class of double perovskite materials hold great potential for enabling high-performance radiation detection with a competitive cost advantage. Our experiment results revealed a bandgap of 2.07 eV of as-grown Cs2AgBiBr6 using the Tauc method.  The resistivity decreased from 1×1010 Ω/cm to 5×107 Ω/cm when the temperature was increased from 25 °C to 80 °C. Furthermore, the resistivity increased to 2×1010 Ω/cm after the high-temperature treatment.  The space-charge-limited-current analysis indicated the trap density and the carrier mobility of Bi-poor Cs2AgBiBr6 are 8.52×1010 cm-3  and 1.52×10-2 cm2/V∙s , respectively. Additionally, the temporal response of Cs2AgBiBr6 crystal under 568-nm LED illumination showed that the rise time and decay time after high-temperature measurements are much shorter than the initial values. These results indicate high temperature treatment could play an important role in tuning the fast decaying and rising time characteristics of Cs2AgBiBr6.

Keywords: Perovskites, Radiation Detectors, Resistivity, Temperature, Cs2AgBiBr6
8:00 AM R-10-05

Space charge optical manipulation in CZT detectors (#544)

E. Belas1, R. Grill1, J. Pipek1, P. Praus1, M. Betusiak1, K. Iniewski2

1 Charles University, Institute of Physics, Faculty of Mathematics and Physics, Prague 2, Czech Republic
2 Redlen Technologies, V8M 0A5 Saanichton, British Columbia, Canada


Semiinsulating CdZnTe is one of the most important semiconductors for fabrication of room-temperature radiation detectors. One of the key problems of the higher commercialization of CZT detectors is the space charge formation within the detector due to the trapping of charge carriers on the deep defect levels resulting in the disturbing of the internal electric field and sensor polarization. In this work, we present the method of the space charge manipulation in the high quality p-type indium-doped CdZnTe detector with Pt/Pt Schottky electrodes using additive anode continuous above bandgap LED illumination. New defect model explaining the space charge formation and internal electric field distribution is developed and successfully applied. For the characterization of the space charge formation, we used the Time-of-flight spectroscopy using laser-induced transient current technique (L-TCT). All experimental results are subjected to the theoretical analysis based on the Shockley-Read-Hall trap assisted recombination model and the solution of the drift–diffusion and Poisson equations using the Monte Carlo simulation.
We found that the detector leakage current was significantly eliminated using Schottky electrodes, however negative space charge is formed rather fast due to the hole depletion. We observed that the value and polarity of the space charge can be changed using the continuous anode LED illumination (wavelength 670nm) with variable intensity. When the photocurrent density reaches values around -150 nA/cm2, we observed zero space charge throughout the sample i.e. nearly constant internal electric field. Further increase of the LED intensity leads to the formation of the positive space charge and to the increase of the electric field beneath the cathode.

AcknowledgmentThis work was supported by the Grant Agency of the Czech Republic under the contract No. 19-11920S and by the Grant of Charles University under the contract No. SVV-2020-267306.
Keywords: CdZnTe, TOF, Space charge, Detector polarization
8:15 AM R-10-06

Comparative Studies of CdZnTe, CdMnTe, and CdZnTeSe Materials for Room-Temperature Nuclear Detection Applications (#1272)

S. U. Egarievwe1, 2, S. D. Soto1, 3, S. W. Sykes1, 3, L. J. Fuller1, 3, Q. J. Alsbrooks1, 3, M. A. Alim1, 3, U. N. Roy2, 6, E. O. Agbalagba4, M. L. Drabo1, 5, R. B. James6

1 Alabama A&M University, Nuclear Engineering and Radiological Science Center, Huntsville, Alabama, United States of America
2 Brookhaven National Laboratory, Nonproliferation and National Security, Upton, New York, United States of America
3 Alabama A&M University, Electrical Engineering & Computer Science, Huntsville, Alabama, United States of America
4 Federal University of Petroleum Resources, Department of Physics, Effurun, Nigeria
5 Alabama A&M University, Mechanical Engineering, Huntsville, Alabama, United States of America
6 Savannah River National Laboratory, Science and Technology, Aiken, South Carolina, United States of America


Cadmium telluride (CdTe) and its ternary and quaternary compounds have found applications in the development of X-ray and gamma-ray detectors used in nuclear detection and medical imaging applications. Example of these detectors include CdZnTe (CZT), CdMnTe (CMT), and CdZnTeSe (CZTS). These nuclear detectors can operate at room temperature without cryogenic cooling. This paper presents comparative studies of these semiconductor material. The properties studied include detector resistivity, Te inclusions, grain boundary networks, mobility/lifetime of the charge carriers, and energy resolution. The effects of passivation with chemicals such as KOH and NH4F, are also presented. X-ray photoelectron spectroscopy (XPS) studies showed increase in the quantity of TeO2 on surfaces of these materials after passivation in KOH and NH4F. While CZT detector has wide commercial availability, it has more Te inclusions and grain boundary network compared to CZTS. CMT and CZTS have better crystal uniformity than CZT. The comparatively low presence of Te inclusions and grain boundary network in CZTS gives it a higher crystal growth yield for detector-grade material.

AcknowledgmentThis work was supported in part by the National Science Foundation (NSF) Major Research Instrumentation (MRI) through award number 1726901; in part by U.S. Department of Energy (DOE), Office of Defense Nuclear Nonproliferation Research and Development, the DNN R&D (NA-22), and DOE NNSA MSIPP award number DE-NA0003980; in part by the U.S. Nuclear Regulatory Commission (NRC) through award 31310018M0035; in part by the U.S. Department of Homeland Security, Domestic Nuclear Detection Office through award number 2012-DN-077-ARI065-05; and in part by the NSF HBCU-UP Program through award number 1818732.
Keywords: CdMnTe, CdZnTe, CdZnTeSe, Gamma rays, Nuclear detectors
8:30 AM R-10-07

RTSD Concluding Remarks (#317)

R. B. James1, T. Takahashi2

1 Savannah River National Laboratory, Science & Technology Directorate, Aiken, South Carolina, United States of America
2 The University of Tokyo, Kavli IPMU, Chiba, Japan


Concluding Remarks:

We will hit some of the highlights of the 2021 RTSD. TBD

Clearly, many challenges remain, but the investigations reported at this meeting and the understanding that has emerged from these studies continues to pave the road to realization of new devices.

This meeting has truly presented a special opportunity for us to share knowledge, energy and experience with our colleagues engaged in similar work.  Before adjourning, Professor Takahashi and I would like to offer a special thanks to all of the speakers, the sponsors, and those who contributed to lively, participative discussions.  This concludes the 28th International Symposium on Room-Temperature Semiconductor X- and Gamma-Ray Detectors.

Keywords: RTSD, Concluding Remarks

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