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## Creator

[M. Togawa](https://orcid.org/0000-0002-1128-4200), S. Fujii, [M. Imura](https://orcid.org/0000-0002-4236-9549), K. Itabashi, T. Isobe, M. Miyahara, J. Nishinaga, H. Okumura

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© 2024 IOP Publishing Ltd and Sissa Medialab<br>
This is an author-created, un-copyedited version of an article accepted for publication/published
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## Other metadata

[The CIGS semiconductor detector for particle physics](https://mdr.nims.go.jp/datasets/176fdf38-d94d-4fa3-9ada-ca3dd9c232f2)

## Fulltext

Prepared for submission to JINST124th international Workshop on Radiation Imaging Detectors, iWoRiD22023325 - 29, June, 20234Oslo Science Park5The CIGS semiconductor detector for particle physics6M. Togawa, 0,1,1 S. Fujii,2 M. Imura,3 K. Itabashi,1 T. Isobe,4 M. Miyahara,0,1 J.7Nishinaga, 5 and H. Okumura680Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization (KEK), Tsukuba,9Ibaraki 305-0801, Japan.101International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles11(QUP, WPI), Tsukuba, Ibaraki 305-0801, Japan.122The Graduate University for Advanced Studies, SOKENDAI, Kanagawa, Japan.133Research Center for Functional Materials, National Institute for Material Science (NIMS), Tsukuba, Ibaraki14305-0044, Japan.154Institute of Physical and Chemical Research (RIKEN), Wako, Saitama, 351-0198, Japan.165 Research Institute for Energy Conservation, National Institute of Advanced Industrial Science and Tech-17nology (AIST), Tsukuba, Ibaraki 305-8568, Japan.186Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan.19E-mail: manabu.togawa@kek.jp20Abstract: Silicon is commonly used as a sensor material in a wide variety of imaging application.21In recent high-energy and intensity beam experiments, high radiation tolerance is required, and22new semiconductor detector consisting of radiation-hard materials have been investigated. The23Cu(In,Ga)Se2 (CIGS) semiconductor is expected to possess high radiation tolerance, with the ability24to recover from radiation damage through the compensation of defects by ions. The CIGS has25originally developed for a solar cell and its radiation tolerance was investigated for the usage in26space. The CIGS, featuring a recovery capability, would shed new light to particle detecror in high27radiation environments. CIGS detectors (2 and 5 `m thick) were tested by Xe ion (400 MeV/u,28132Xe54+) at HIMAC, successfully detecting single Xe ion with a fast response. The output charge29is understandable through estimation with the GEANT4 simulation. With 0.6 MGy irradiation by30Xe ions, the CIGS output degraded to 50%, but it was recovered to 97% after the heat treatment31under 130 ◦C for 2 hours. This marks a significant step in confirming that CIGS semiconductors32can serve as particle detectors with recovery features for radiation damage.33Keywords: Radiation-hard detectors, Radiation damage to detector materials (solid state), Mate-34rials for solid-state detectors35ArXiv ePrint: 1234.5678936¹Corresponding authormailto:manabu.togawa@kek.jphttps://arxiv.org/abs/1234.56789Contents371 Introduction 1382 The CIGS detector 2393 Experimental Setup at HIMAC 2404 Results 3414.1 Signal output 3424.2 Leakage current 4435 Conclusion 5441 Introduction45Silicon is commonly used as a sensor material in wide variety of imaging application. In recent46high energy and intensity beam experiments, high radiation tolerance is required. The semiconduc-47tor detectors, particularly those used in hadron colliders, receive the highest radiation in particle48physics experiments. These detectors, placed around the collision point to track particles, endure49damage from these collisions. The Large Hadron Collider (LHC), the world’s highest energy and50intensity proton collider, is planing a higher luminosity upgrade, with the radiation levels assum-51ing 1016 MeV neq/cm2 and 7 MGy for Non Ionization Energy Loss (NIEL) and Total Ionization52Dose (TID), respectively. To withstand such high dose levels, detectors have been developed with53novel electrode structures, such as 3-D sensors, for example [1]. In anticipation of future hadron54collider experiments, the development of higher radiation-tolerant detectors with new innovations55is necessary.56A new semiconductor detector based on radiation hard material has been developed. Wide-gap57semiconductors, such as Diamond [2] and Gallium Nitride [3], has been investigated globally due58to their high binding energy among nucleons and low leakage current. The Cu(In,Ga)Se2 (CIGS)59semiconductor is also expected to have high radiation tolerance coupled with a unique feature, re-60covery through the compensation of defects by ions. Originally developed for solar cells, CIGS’s61radiation tolerance was initially investigated for space applications [4]. As a preliminary experi-62ment, CIGS solar cells were irradiated with 1016 MeV neq/cm2 and 7 MGy by 70 MeV proton beam63at the Cyclotron and Radioisotope Center (CYRIC), Tohoku University. The CIGS solar cells de-64teriorated after proton irradiation, with decreased conversion efficiency and short-circuit current65density. However, both parameters were gradually recovered through heat-light annealing [5].66This paper describes the demonstration of the world’s first CIGS detector, taking advantage of67its recovery feature for radiation hardness.”68– 1 –2 The CIGS detector69The CIGS detector and its layer configuration are shown in Figure 1. The geometries of CIGS70detectors are approximately 5×4 mm2, and the thicknesses of active layer (CIGS layer) are 2 or 571`m. CIGS is a p-type semiconductor and the CdS/ZnO is connected as n-type for the p-n junction.72In this detector, two n-type electrodes are prepared for signal read out. More details are described73in [5]. The depletion voltage is supplied from CIGS side with -2.0 V and the typical leakage current74is about 1 nA.75Since these new detectors have thin active layer, so far only 2 or 5 `m, the detection of single76charged particle is challenging due to very small charge outputs. A heavy ion beam is a better choice77to test such condition since charge outputs are expected to be large. Of cause, the new detector would78be a good candidate as a heavy ion tracker, which also requires radiation tolerance. The expected79charge inducing by the penetration of a 400 MeV/u 132Xe54+ beam on the 2 `m thick detector is80estimated by the GEANT4 simulation yielding a value of about 280 fC.81Figure 1. A CIGS detector configuration for 2 `m active thickness. Signals are read out from n-type CdSelectrodes under home-base shaped Al pads for wirebonds.3 Experimental Setup at HIMAC82For demonstration of the CIGS detector, a heavy ion beam, Xe ion (400 MeV/u, 132Xe54+) at the83Heavy Ion Medical Accelerator in Chiba (HIMAC) was selected. We used the PH2 beam line, and84the experimental setup is shown in Figure 2. Only detectors were positioned on the beam axis, with85the readout circuits, including signal amplification, placed next to the detector. The beam size was86adjusted to approximately q 3-5 mm using a fluorescent plate at the beginning. To induce irradiation87damage, the beam power was set to 107 particles per pulse (ppp) within 3.3-second pulse cycles.88The number of Xe beam was monitored by scintillator counter placed off-beam position.89– 2 –Figure 2. A setup photo at the PH2 beam line. Only detectors were placed on the beam.4 Results904.1 Signal output91The outputs from the CICS detector are shown in Figure 3. The data were recorded using the92waveform digitizing function in the readout ASIC, and the signal response looks sharp. The charge93generated by Xe ion penetration can be estimated by integrating the wave form signal (Integrated94ADC). The charge is approximately 180 fC and this value is 64% of the estimation by the GEANT495simulation. Possible considerations are low charge collection efficiency and/or the excitation density96effect, but further investigations are needed for a conclusive understanding. We also irradiated the975 `m thick CIGS detector and the output is about 2.5 times larger than that of 2 `m thick, as we98expected.99In Figure 4, the history of Integrated ADC value normalized to the value of un-irradiated are100plotted. The conditions were changed in five periods as followings,101(1) 0-16 h : Irradiation of Xe ion, 0.6 MGy in total : The output decreased to be 0.5,102(2) 18-20 h : Heat annealing with 130 ◦C : The output recovered to be 0.97,103(3) 20-27 h : Irradiation of Xe ion, 0.2 MGy in total : The output decreased to be 0.8,104(4) 28-31 h : Heat annealing with 90 ◦C : The output was not changed,105(5) 31-33 h : Heat annealing with 130 ◦C : The output recovered to be 0.94.106It is confirmed the CIGS detector deteriorates in terms of signal output, likely due to the reduction107of charge collection efficiency by defects generated by irradiation. With heat annealing at 130 °C,108the signal output almost returned to the initial value. The recovery shows no limits up to 0.8 MGy109– 3 –and is repeatable. Since there was no significant recovery with 90 ◦C within this time period, the110recovery appears to have strong temperature dependence between 90 and 130 ◦C.111Figure 3. Left) Signal from single Xe ion event. The event is recorded by the wave form digitizing. Right)Integrated ADC values of recorded events. It is clearly separation of hit and no-hit.Figure 4. The output history of the CIGS detector.4.2 Leakage current112The leakage current during 27-hour period, corresponding to periods of (1) to (3) in section 4.1, is113shown in Figure 5. The leakage current increased proportionally to the amount of Xe irradiation114– 4 –from 1 nA to 35 nA. After the heat annealing, the current returned to 3 nA, nearly reaching the115initial value. With additional Xe irradiation, the leakage current increased with same tendency in116period of (1).117Based on the results of signal output and leakage current, it can be inferred that recombination118centers generated by radiation damage are passivated by heat annealing.119Figure 5. The leakage current history of the CIGS detector.5 Conclusion120For the particle detector in a high radiation environment, we have developed new semiconductor121detectors using CIGS. The 2 `m thick detector was irradiated by Xe ions and it successfully detected122a single Xe ion particle with a fast response. For the accumulation of radiation damage, Xe beam was123irradiated up to 0.8 MGy. It has been confirmed that the decreased signal outputs can be recovered by124heat annealing at 130 ◦C, and the recovery is repeatable. This marks a major milestone in realizing125the CIGS particle detector with a recovery mechanism. Since there was no significant recovery at 90126◦C within this time period, the recovery appears to have a strong temperature dependence between12790 and 130 ◦C.128Acknowledgments129This work was partly supported by the Tsukuba Innovation Arena (TIA) “Kakehashi” and JSPS130KAKENHI Grant No. 21K18635 and 23H01191 from the Ministry of Education, Culture, Sports,131Science and Technology (MEXT), Japan. This work was supported by World Premier International132Research Center Initiative (WPI), MEXT, Japan. Part of the experiments was performed under the133– 5 –Research Project with Heavy Ions at NIRS-HIMAC, program No. 21H455. The authors also wish134to thank the accelerator staff at HIMAC for supplying the excellent beams used in this work.135References136[1] The ATLAS Collaboration, Technical Design Report for the ATLAS Inner Tracker Pixel Detector,137CERN-LHCC-2020-007 ; ATLAS-TDR-031. (2017)138[2] H. Kagan, 4C 0;., Diamond detector technology, status and perspectives, Nucl. Instrum. and Meth. A139924 (2019) 297140[3] H. Okumura, 4C 0;., Degradation of vertical GaN diodes during proton and xenon-ion irradiation,141Jpn. J. Appl. Phys. 62, (2023) 064001.142[4] S. Kawakita, 4C 0;., Annealing enhancement effect by light illumination on proton irradiated143Cu(In,Ga)Se2 thin-film solar cells, Jpn. J. Appl. Phys. 41, (2002) L797-L799 .144[5] J. Nishinaga 4C 0;., Annealing effects on Cu(In,Ga)Se2 solar cells irradiated by high-fluence proton145beam, Jpn. J. Appl. Phys. 62 (2023) SK1014.146– 6 – Introduction The CIGS detector Experimental Setup at HIMAC Results Signal output Leakage current Conclusion