IEEE 2021 NSS MIC

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RTSD POSTERS

Session chair: Niraula , Madan (Nagoya Institute of Technology, Graduate School of Engineering, Nagoya, Japan)
 
Shortcut: R-04
Date: Tuesday, 19 October, 2021, 11:45 AM - 1:45 PM
Room: RTSD
Session type: RTSD Session

Contents

Click on an contribution to preview the abstract content.

R-04-01

First Prototype of a 3-D Position-Sensitive TlBr Gamma-Ray Spectrometer (#118)

F. Zhang1, M. Streicher1, H. Kim2, C. Leak3, E. Hall3, J. Christian2, L. Cirignano2, K. Shah2, Z. He3

1 H3D, Inc., Ann Arbor, Michigan, United States of America
2 RMD, Inc., Watertown, Massachusetts, United States of America
3 University of Michigan, Department of Nuclear Engineering and Radiological Sciences, Ann Arbor, Michigan, United States of America

Abstract

A 12×12×5 mm3 TlBr detector with 11×11 pixelated anodes were assembled into a S100x compact prototype gamma-ray spectrometer. A single-pixel energy resolution of 2.2% FWHM at 662 keV has been obtained from all 121-pixel anodes after three-dimensional signal correction. An energy resolution of 1.5% FWHM is recorded on the best performing pixel anode. Signals induced on the 121-pixel anodes and the planar cathode were readout using a 130-channel digital charge-sensing ASIC manufactured by IDEAS in Oslo. The recorded signal waveforms were digitally processed to generate gamma-ray spectra. The S100x system manufactured by H3D, Inc. provides a readout platform that can accommodate different semi-conductor detector materials with firmware modifications, including CZT.

Acknowledgment

This work conducted under the auspices of the U.S. Department of Homeland Security, Countering Weapons of Mass Destruction Office, under competitively awarded contract 70RDND18C00000019. This support does not constitute an express or implied endorsement on the part of the US Government.

Keywords: gamma-ray detectors, semiconductor radiation detectors, thallium bromide, TlBr
R-04-02

Growth and characterization of single-crystal lead halide perovskite for X-ray detector application (#182)

M.M. Islam1, M. Niraula1, Y. Nakashima1, T. Matsubara1, S. Hirano1, Y. Takagi1, K. Yasuda1

1 Nagoya Institute Of Technology, Graduate School of Engineeing, Gokiso, Showa,Nagoya 466-8555, Japan

Abstract

In this study, the growth of methylammonium lead iodide (CH3NH3PbI3) single crystal for X-ray detector application has been reported. The inverse temperature crystallization (ITC) technique was employed to grow large-size bulk crystals by repeated seeding. By optimizing the molar ratio and maintaining ambient conditions, up to 10 mm ×  10 mm ×  3 mm dimension crystals were obtained. We polished the surface of the crystal with different grade sandpaper to make it smooth. The powder XRD (PXRD) result of the grown crystals confirmed the synthesis and structure of the crystals. The optical bandgap of the grown crystals was 1.51 eV as confirmed by transmittance measurement. We further evaporated the gold electrode on both sides of the crystal to fabricate the detector. The bulk resistivity of the crystal was around 2 ×108 Ω cm, which was calculated by performing current-voltage (I-V) measurement at room temperature and in dark conditions. We also confirmed the photo response of the detector by irradiating a low-power commercial LED. Further detector characterization is underway and the details will be presented at the meeting.

Keywords: Metal halide perovskite, Bulk crystal, X-ray detector
R-04-03

Unravelling the electronic and charge transport properties in organic perovskites (#254)

M. Brynza1, E. Belas1, J. Pipek1, M. Betušiak1, P. Praus1, M. Ahmadi3, R. Grill1, A. Musiienko2, 1

1 Charles University, Institute of Physics, Faculty of Mathematics and Physics, Prague, Czech Republic
2 Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin, Berlin, Germany
3 University of Tennesse, Joint Institute for Advanced Materials, Department of Materials Science and Engineering, Tennessee, Tennessee, United States of America

Abstract

Halide perovskites have made an appearance as a promising optoelectronic material that can be used in a wide variety of applications. Several studies draw attention to the critical role of the defects on the efficiency of perovskite optoelectronics. This study investigated the dynamics of free holes in methylammonium lead tribromide perovskite (MABbBr3) single crystals using the time-of-flight (ToF) current spectroscopy. Using Monte Carlo simulations, we characterise the charge carrier’s relaxation and effect of traps on charge transport. We identified three energy levels and their trapping and detrapping rates. We demonstrate the considerable effect on the transport properties of MABbBr3 single crystals, including mobility and lifetime of the carriers. Our study gives an insight into the charge transport properties of perovskite semiconductors and critical parameters of radiation sensors.

AcknowledgmentI would like to thank the Institute of Physics of Charles University for providing the necessary facilities to conduct this research. Acknowledge financial support from the Grant Agency of Charles University, project no.379621 and project no.1234119. 
Keywords: perovskites, time-of-flight, Monte Carlo
R-04-04

Charge transport in TlBr radiation detectors (#397)

M. Betusiak1, E. Belas1, R. Grill1, M. Brynza1, J. Pipek1, P. Praus1, H. Onabe2

1 Charles University, Insitute of Physics of Charles University, Prague 2, Czech Republic
2 Raytech Corporation, Utsunomiya, Japan

Abstract

Recent progress in thallium bromide purification led to a dramatic increase in mobility-lifetime product, which is now comparable to that of cadmium zinc telluride. Identification of the extrinsic defects is therefore a key step in the material purification process. The carrier transport properties were studied and evaluated using the laser-induced transient current technique and Monte-Carlo simulation in this work. Temporal stability measurement conducted at pulsed bias revealed the presence of deep electron and hole trapping centre with low concentration.

Keywords: Thallium Bromide, Time-of-Flight, Laser-induced Transient Current Technique
R-04-05

Phantom study of sandwich-structured CZT photon-counting BMD detector (#404)

B. Park1, 3, J. Seo1, 3, J. Byun1, 3, K. Kim2

1 Korea University, Department of health and safety convergence science, Seoul, Republic of Korea
2 Korea University, School of health and environmental science, Seoul, Republic of Korea
3 Korea University, Interdisciplinary Program in Precision Public Health, Seoul, Republic of Korea

Abstract

The dual energy X-ray absorption (DEXA) is conventional method which measure the bone mineral density (BMD). Instead of DEXA method, sandwich-structured CdZnTe (CZT) detector employed to measure the bone mineral in accurate and in low dose with an high energy X-ray only. Front CZT detector with 0.75-mm  and rear CZT detector with 3-mm are optimized in low energy and high energy detection, respectively. In the spectroscopy of radio-isotope with sandwich-structured CZT detector, front and rear detector exhibit different response depending on the gamma-ray energy. Also, phantom studies with L-4 spine of the vertebra phantom provided an image of L4 spine and BMD value of 1.195 g/cm2 with an error of 0.42%. The real value of vertebra phantom is 1.2 g/cm2.

AcknowledgmentThis work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (MSIT) (No. 2018M2A2B3A01072384) and (No. 2021R1A2C1012161)
Keywords: Sandwich-structured CdZnTe detector, BMD, photon counting, DEXA
R-04-06

Identifying radionuclides in groundwater using a linear regression analysis applied to spectra collected with a CdTe in-situ detector (#540)

G. Turkington1, K. A. Gamage1, J. Graham2

1 University of Glasgow, Electronics & Engineering, Glasgow, United Kingdom
2 National Nuclear Laboratory, Seascale, United Kingdom

Abstract

This research aims to develop a methodology for estimating the 90Sr contribution to total activity in a groundwater at nuclear decommissioning sites as measured by cadmium telluride (CdTe) detector which is deployed into a groundwater borehole.
There is demand in the nuclear decommissioning industry to develop new beta radiation detection techniques which can reduce the lifetime monitoring costs for radionuclide contamination in the environment.
The aim is to design techniques which are safer, produce less secondary waste and can be completed rapidly without the need for specialised laboratory techniques.
Currently, groundwater samples are taken from underground boreholes, treated, placed into storage and eventually the radionuclides in the groundwater are analysed using radiochemical separation and liquid scintillation counting.
However, these stages could be by-passed with the deployment of an in-situ semiconductor detector. This paper reports on the application of a linear regression analysis to Monte Carlo simulations of the detector's response to radionuclides in groundwater.  This technique allows for the activity of individual radionuclides to be determined using a gross measurement of the activity in the borehole.

Keywords: cdte, detector, nuclear, decommissioning, spectroscopy
R-04-07

Low Temperature Annealing of CdTe Detectors with Evaporated Gold Contacts and its effect on Detector Performance (#679)

M. Niraula1, K. Yasuda1, Y. Takagi1, S. Fujii1

1 Nagoya Institute of Technology, Dept. Elect. and Mech. Engg, Nagoya, Japan

Abstract

Annealing is usually performed after contact deposition in order to improve adhesion of metal onto the semiconductor crystal. In this study, we investigated the effect of annealing on the detector current, gamma detection property and its response stability. Detectors were fabricated by evaporating gold electrodes on both sides of a high resistivity (111) CdTe bulk crystal, as well as using an epitaxially grown thick CdTe based p-CdTe/n-CdTe/(211)n+-Si hereojunction diode type detectors.    After detector fabrication they were subjected to annealing in a hydrogen atmosphere, where the annealing temperature and anneal time were varied from 100 to 300 oC, and 30 to 120 sec, respectively.  Performance of these annealed detectors were evaluated and compared with that of a similar type of detector that was not subjected to anneal. All bulk detectors or epi-based detectors studied were obtained by cutting from respective large detectors. It was found that detector performance and their stability improve remarkably after annealing for bulk detectors, however, the improvement was moderate for the epi-based detectors. These results and their probable causes will be discussed.

Acknowledgment

Part of this work was supported by JSPS Kakenhi, Grant no. 20K04619.

Keywords: CdTe detectors, annealing, stability
R-04-08

Feasibility studies of NaOCl as a wet passivant for CdZnTeSe detectors (#743)

J. Seo1, 3, B. Park1, 3, J. Byun1, 3, K. Kim2

1 Korea University, Department of health and safety convergence science, Seoul, Republic of Korea
2 Korea University, School of health and environmental science, Seoul, Republic of Korea
3 Korea University, Interdisciplinary program in precision public health, Seoul, Republic of Korea

Abstract

Chemical etching with Bromine solutions leaves conductive Te-rich layers on the CdZnTeSe(CZTS) materials due to the selective etching properties. Those Te-rich layers deteriorate the performance of CZTS detector by increasing leakage current and surface recombination velocity. New passivant, sodium hypochlorite (NaOCl), was applied in the passivation of CZTS detector. Optimal passivation time was determined from the surface and bulk resistivity and the energy resolution of detector on Am-241. In addition, the state of Te atoms before and after passivation was evaluated with the X-ray photoelectron spectroscopy (XPS) measurement. The CZTS detector passivated with NaOCl for 90 s exhibit most low leakage current and high energy resolution for 59.5 keV of Am-241. Also, the detector performance was maintained for 60 days in ambient condition.

Acknowledgment

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (MSIT) (No. 2018M2A2B3A01072384) and (No. 2021R1A2C1012161)

Keywords: Wet passivation, Sodium hypochlorite(NaOCl), Ⅱ-Ⅵ semiconductor materials, CdZnTeSe(CZTS), Room temperature semiconductor detector
R-04-09

Characterization of a 4-hydroxycyanobenzene radiation detector for dose monitoring in carbon therapy (#774)

F. Nishikido1, E. Takada2, M. Yamagishi2, D. Satake2, S. Takyu1, H. G. Kang1, T. Yamaya1

1 National Institutes for Quantum and Radiological Science and Technology, Chiba, Japan
2 National Institute of Technology, Toyama College, Toyama, Japan

Abstract

Organic semiconductors are suitable for dose monitoring in carbon therapy since they are tissue equivalent materials. Here, we have evaluated a 4-hydroxycyanobenzene (4HCB) single crystal as an organic semiconductor radiation detector for carbon therapy. The thickness of the 4HCB crystal can be increased to more than 1 mm easily in order to apply a voltage over 100 V. The 4HCB crystal (4 mm × 4 mm × 2 mm) was mounted on a 10 mm × 10 mm × 1 mm black ABS plate. Readout wires were connected to two sides of the 4HCB crystal with silver paste. The applied voltages to the 4HCB detector were from +10 V to +800 V in the experiment. The experiment was performed in the PH2 course of the Heavy Ion Medical Accelerator in Chiba (HIMAC) at NIRS. The energy and beam intensity of the 12C beam were 290 MeV/u and 1.8 × 109 particles per second (pps). The diameter of the carbon beam was ~1 cm at the detector. The 4HCB detector was irradiated by the carbon beam that was passed through an ionization chamber which was used to normalize the number of irradiated particles.

We clearly observed collected charges in the 4HCB single crystal obtained during each 0.1 s period of the carbon beam irradiation. The beam spill structure of the 3.3 s cycle was also clearly observed. In addition, we obtained normalized induced charges for the carbon beam irradiation as a function of applied voltages to the 4HCB detector (i.e. saturation curve). The optimum voltage was determined at 500 V for the evaluated 4HCB detector.

Keywords: Organic detector, 4-hydroxycyanobenzene, Carbon therapy, 4HCB
R-04-10

A Miniaturized Gamma-ray Spectrometer based on CdZnTe Semiconductor and BGO Scintillator (#781)

Y. Wang1, 2, C. Feng1, 2, P. Lin3, D. Wang1, 2, W. Xie3, Q. Lei3, C. Shan3, M. Zhao1, 2, Z. Zhou1, 2, S. Liu1, 2

1 University of Science and Technology of China, State Key Laboratory of Particle Detection and Electronics, Hefei, China
2 University of Science and Technology of China, Department of Modern Physics, Hefei, China
3 China Nuclear Power Technology Research Institute Co. Ltd., Shenzhen, China

Abstract

A miniaturized gamma-ray spectrometer, which is designed for the applications of gamma-ray measurement, is described in this paper. The detector consists of a 10 mm × 10 mm × 10 mm CdZnTe semiconductor and a Φ51 mm × 60 mm BGO scintillator. With the structure of a CdZnTe module assembled in the cavity of a cup-shaped BGO, the detector has both the function of rapid detection just using BGO, and the functions of angular sensitivity and Compton suppression using CdZnTe with BGO as a collimator and anti-coincidence detector. The characteristics of the detector are estimated by the Monte Carlo simulations. The angular sensitivity is high and the angular response is less than 10% at 10°. For the prototype spectrometer, the readout electronics was designed and the prototype has been developed. Preliminary tests showed that the detector is well coordinated with readout electronics. The energy resolution of 1.8% at 662keV and Compton suppression effect of 30% have been achieved.

Keywords: Angular sensitivity, Compton suppression, Gamma-ray measurement, Miniaturized spectrometer
R-04-11

Investigating the role of Te inclusions in hole-trapping paradox in CdZnTeSe room-temperature gamma detectors (#1220)

S. K. Chaudhuri1, J. W. Kleppinger1, R. Nag1, U. N. Roy2, R. B. James2, K. C. Mandal1

1 University of South Carolina, Department of Electrical Engineering, Columbia, South Carolina, United States of America
2 Savannah River National Laboratory, Materials Directorate and Devices Division, Aiken, United States of America

Abstract

We report for the first time the growth of CZTS single crystals using a modified vertical Bridgman method (VBM) with exceptionally high electron drift mobility. Radiation detectors in planar electrode geometry have been fabricated using the grown crystals, which demonstrated a record high electron drift mobility of 1468 cm2V-1s-1. The detector also showed very high bulk electrical resistivity of 1 × 1011 Ω-cm. The electron mobility-lifetime product was measured to be 2.2 × 10-3 cm2/V through alpha spectrometry. However, the hole transport properties did not show any remarkable improvement over that observed in CZT. Density functional theory (DFT) based calculations confirmed that the addition of Se in the Cd0.9Zn0.1Te matrix helps to reduce the formation of TeCd antisites that act as electron trapping centres, thereby improving the electron transport properties in CZTS substantially. To investigate the paradoxical exhibition of poor hole mobility despite the reduced presence of Te inclusions, both the electron and hole trap centres have been studied using photo-induced current transient spectroscopy (PICTS) in CZTS single crystals grown using VBM and a travelling heater method. Correlation studies of trap centres observed using PICTS with device performance, particularly hole transport properties, will be presented.

AcknowledgmentThe authors acknowledge partial financial support from the DOE Office of Nuclear Energy’s Nuclear Energy University Programs (NEUP), Grant No. DE-NE0008662.
Keywords: CdxZn1-xTeySe1-y (CZTS), room-temperature radiation detectors, charge transport properties, gamma ray detection, photo induced current transient spectroscopy (PICTS).
R-04-12

Spatial Resolution of X-ray Imaging using TlBr Detector with Silver Electrodes (#1244)

K. Toyoda1, K. Takagi2, 1, H. Kase3, 1, T. Takagi3, 1, K. Tabata2, T. Terao1, H. Morii1, A. Koike1, 2, T. Aoki2, 1, M. Nogami4, K. Hitomi4

1 ANSeeN Inc., Hamamatsu, Japan
2 Shizuoka University, Research Institute of Electronics, Hamamatsu, Japan
3 Shizuoka University, Cooperative Major in Medical Photonics, Hamamatsu, Japan
4 Tohoku University, Quantum Science and Energy Engineering, Sendai, Japan

Abstract

This study introduces an X-ray imager that uses TlBr detectors and demonstrates its potential for X-ray imaging applications.
Although TlBr detectors are suitable for X-ray imaging applications because of the associated large attenuation coefficients and direct conversion behavior, realizing a flat-panel detector with TlBr involves developing processes.
The proposed imager is constructed utilizing a combination of existing technologies; it comprises a plate electrode containing thallium metal to suppress the polarization phenomenon, pixelated silver electrodes with 80μm pitch, and a photon-counting-type readout integrated circuit (ROIC) that can work in the hole as well as electron collection modes.
The modulation transfer function (MTF) of the imager is calculated based on the imaging results of an X-ray test chart, and the result corresponds to 180μm sampling.
Even though the imager is not designed specifically for TlBr detectors, the measured high-MTF shows the immense potential of TlBr detectors for X-ray imaging applications.
The results of this study can motivate the development of flat-panel-detector processes optimized for TlBr detectors.

AcknowledgmentThis research was partly supported by AMED under Grant Number JP19hm0102034 and the Cooperative Research Projects of Research Center for Biomedical Engineering, Japan.
Keywords: Thallium bromide, Semiconductor radiation detector, X-ray imaging
R-04-13

Annealing effects on CdTe pn diodes fabricated by laser doping method (#1308)

A. Ohno1, J. Nishizawa2, H. Nakagawa3, K. Takagi3, K. Tabata3, T. Aoki3

1 Shizuoka University, Graduate School of Integrated Science and Technology, Hamamatsu, Japan
2 Shizuoka University, Graduate school of Medical Photonics, Hamamatsu, Japan
3 Shizuoka University, Research Institute of Electronics, Hamamatsu, Japan

Abstract

CdTe semiconductor has been used as radiation detectors at room temperature. Impurity doping of CdTe using ion implantation and other methods has been considered difficult because it requires high temperature heat treatment and characteristics are degraded. In the fabrication of semiconductor detectors using CdTe, Schottky diodes are widely used because pn diodes require impurity doping during fabrication. However, the laser doping method that we have recently developed is overcoming this problem. When doping semiconductors, not all dopants act as donors or acceptors, and some of them become defects in the crystal. In response to the presence of such inactive dopants, for example, ion implantation undergoes an annealing process to promote the activation of the dopants. On the other hand, when CdTe is annealed above 150℃, the characteristics of diodes and detectors are degraded, such as increased reverse current and decreased hole mobility. Therefore, annealing has been considered difficult for CdTe. The I-V characteristics of CdTe pn diodes doped by laser-induced backside doping do not degrade when heat-treated above 150℃, and in fact I-V characteristics are improved. Therefore, it was assumed that annealing of CdTe might be possible because the characteristic degradation due to annealing that has been reported could not be measured. The CdTe pn diodes fabricated by the laser doping method was annealed and investigated the annealing effect. The annealing process was carried out from 100℃ to 1000℃. CdTe was doped In by direct laser irradiation the interface between CdTe and In layer. CdTe schottky diodes In/CdTe/Au fabricated also and compared with CdTe pn diodes. The detector showed that the charge collection efficiency improved with increasing annealing temperature, at least up to 300℃.The I-V characteristics showed no degradation of the diode characteristics such as an increase in reverse current due to heating at least up to 300℃.

Keywords: CdTe, annealing effect, X-ray imaging detector
R-04-14

Evaluation of charge-sharing between pixels of X-ray measurement using photon counting method (#1325)

T. Takagi1, 2, K. Takagi1, 2, A. Ohno4, 2, J. Nishizawa3, 2, K. Tabata1, H. Morii2, A. Koike2, 1, T. Aoki1, 2

1 Shizuoka University, Research Institute of Electronics, Hamamatsu, Japan
2 ANSeeN Inc., Hamamatsu, Japan
3 Shizuoka University, Cooperative Major in Medical Photonics, Hamamatsu, Japan
4 Shizuoka University, Graduate School of Integrated Science and Technology, Hamamatsu, Japan

Abstract

Photon counting detectors have the advantages of high sensitivity, low noise, and possible to energy discrimination compared to the conventional energy integrating detectors. However, under high radiation such as in medical CT, it is difficult to measuring radiation due to pile-up. It is possible to reduce the pixel area as a measure against pile-up, but one of problems is charge sharing. This effect occurs between nearby pixels, causing lower resolution, lower energy resolution, and so on; However, it is rarely evaluated quantitatively. Therefore, in order to quantitatively evaluate charge sharing, we have developed detectors for evaluating pulse signals of multiple pixels in parallel using spectrometers or oscilloscopes. First detector is a single-pixel detector with a small detection area and a guard ring. The detector was made of CdTe with a thickness of 0.75mm. It was confirmed that the number of counts decreased as the detection area became smaller and it was almost proportional to the detector area. However, measured high-energy peaks were collapsed, which was the peaks intensity decreased and the FWHM increased due to charge sharing between the pixel and the guard-ring. Next, a pixelated detector which has nine 100μm pitch pixels has been prepared to measure how charge sharing occurs depending on the difference of neighboring pixels and the distance from the guard-ring. The detector has nine 80μm×80μm electrodes placed on the surface of the CdTe in a 3×3 configuration, and surrounded by the guard ring. By applying the same voltage to each pixel and the guard ring, the actual detection area is 100μm×100μm per pixel. Each pixel connects to a charge sensitive preamplifier in parallel, and individual signals can be measured simultaneously in order to consider the charge transfer. We will discuss the results of quantitative evaluation of charge sharing by comparing the measurement results of the center pixel and the peripheral pixels.

Keywords: Semiconductor radiation detectors, Charge sharing
R-04-15

ASTENA’s Polarimetric Prospects (#1347)

M. Moita1, L. Ferro1, E. Caroli2, E. Virgilli2, R. Curado da Silva3, 5, N. Auricchio2, S. del Sordo6, J. Maia3, 4, J. Stephen2, F. Frontera1

1 University of Ferrara, Dept. of Physics and Earth Science, Ferrara, Italy
2 OAS of Bologna INAF, Bologna, Italy
3 Laboratório de Instrumentação e Física Experimental de Partículas - LIP, Coimbra, Portugal
4 University of Beira-Interior, Physics Department, Covilhã, Portugal
5 University of Coimbra, Physics Department, Coimbra, Portugal
6 IASF - Palermo INAF, Palermo, Italy

Abstract

The measurement of the polarization of the high-energy photons from cosmic sources has now become a key observational parameter for understanding the emission mechanisms and the geometry of the active regions involved. Therefore, a mandatory requirement for new instrumentation in this energy regime will be to provide high sensitivity for polarimetric measurements associated to spectroscopy and imaging. In this perspective, the Advanced Surveyor of Transient Events and Nuclear Astrophysics (ASTENA) mission concept, proposed for the ESA Voyage 2050 planning, is under study. ASTENA includes two main instruments: the Wide field monitor (WFM-IS), with a large effective area and a broad energy passband (2-20 MeV); and the Narrow Field Telescope (NFT), that is a focussing telescope based on an advanced Laue lens with a broad energy passband (50-700 keV), coupled with a high performance CZT focal plane. Both these instruments provide high sensitivity for polarimetric measurements. In fact, they implement spectrometers with a good 3D spatial resolution, allowing to perform reliable 3D Compton polarimetric measurement, by improving the possibility to optimize the event selection. Herein, we report on the results of a Monte Carlo study devoted to optimize the configuration of both instruments as scattering polarimeters. In particular, we present the modulation factor (Q), the events detection efficiency (Eff) and the Minimum Detectable Polarization (MDP), and the dependence of these parameters from detector geometrical configurations (pixel/voxel shape, pixel/voxel scales), and from various filters that can be implemented.

Keywords: Scattering polarimetry, Monte Carlo simulation, Laue Lens, X- and γ-astronomy, 3D spectrometers
R-04-16

Defect Structure and Spectroscopic Properties of CdTe-based X- and Gamma-Ray Detectors (#1402)

O. L. Maslyanchuk1, M. M. Solovan1, I. R. Boledzyuk1, I. M. Fodchuk1, V. A. Gnatyuk2, T. Aoki3

1 Yury Fedkovych Chernivtsi National University, Chernivtsi, Ukraine
2 V.E. Lashkaryov Institute of Semiconductor Physics of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
3 Research Institute of Electronics, Shizuoka University, Hamamatsu, Japan

Abstract

Cadmium telluride is a widely used and still promising material for room-temperature X- and gamma-ray detectors proposed for environmental, medical, security, astrophysics, and other applications. CdTe can potentially provide high resistivity, low leakage current, and high charge-collection efficiency. However, commercial CdTe crystals are affected by structure defects limiting the application of the semiconductor in the production of X- and gamma-ray detectors. In this work, we have tested several kinds of CdTe samples produced by Acrorad, in order to understand the roles of structural defects and their effect on the final detector performance. A complex of techniques, including preliminary chemical and ion surface processing, laser surface treatment, metallization, and surface passivation, were employed during contact preparation. The X-ray diffraction investigations of the defect structure of CdTe crystals and CdTe-based heterostructures were carried out on every stage of the detector fabrication. Various metal contacts (Mo, Ni, In, Al, Ti, and Au) as well as NiO, MoO, TiO, and TiN with different deposition techniques (DC reactive magnetron sputtering and vacuum thermal evaporation) were formed on the similar crystals, and the electrical and spectroscopic properties of the fabricated detectors were investigated.

Keywords: CdTe crystal, Charge transport, Heterostructure, Surface treatment, X/γ-ray detector

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