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[JINST___Journal_of_Instrumentation_template.docx](https://mdr.nims.go.jp/filesets/fdae8b2c-6693-47d6-9938-853d59bbcd71/download)

## Creator

[K. Itabashi](https://orcid.org/0000-0002-6766-4704), [M. Togawa](https://orcid.org/0000-0002-1128-4200), [J. Nishinaga](https://orcid.org/0000-0001-6059-1269), [M. Miyahara](https://orcid.org/0000-0002-5748-5921), [H. Okumura](https://orcid.org/0000-0002-5464-9169), [M. Imura](https://orcid.org/0000-0002-4236-9549), [T. Isobe](https://orcid.org/0000-0001-5163-030X)

## Rights

This is the Accepted Manuscript version of an article accepted for publication in Journal of Instrumentation.  IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it.  The Version of Record is available online at https://doi.org/10.1088/1748-0221/20/06/C06023.[Creative Commons BY-NC-ND Attribution-NonCommercial-NoDerivs 4.0 International](https://creativecommons.org/licenses/by-nc-nd/4.0/)

## Other metadata

[Development of high radiation tolerance detector with CIGS](https://mdr.nims.go.jp/datasets/49751aeb-754b-4245-9b7e-be1a74f47c57)

## Fulltext

1 Prepared for submission to JINST2 Development of high radiation tolerance detector 3 with CIGS4 K. Itabashi1 M. Togawa1,2 J. Nishinaga3 M. Miyahara1,2 H. Okumura4 M. Imura55 T. Isobe61International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles67 (QUP,WPI), High Energy Accelerator Research Organization (KEK), Oho 1-1, Tsukuba, Ibaraki 3058 0801, Japan.2Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization (KEK), Tsukuba, 910 Ibaraki 305-0801, Japan.3Global Zero Emission Research Center, National Institute of Advanced Industrial Science and Technology1112 (AIST), Tsukuba, Ibaraki 305-8568, Japan. 4Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan.135Research Center for Electronic and Optical Materials, National Institute for Material Science (NIMS),1415 Tsukuba, Ibaraki 305-0044, Japan. 6Institute of Physical and Chemical Research (RIKEN), Wako, Sitama, 351-098, Japan.1617 E-mail: kosuke.itabashi@cern.ch18 Abstract: We have been developing a CIGS detector for particle detection with high radiation 19 tolerance. We irradiated the CIGS detector with a 132Xe54+ ion beam, delivering a total ionizing20 dose (TID) of 0.6 MGy at the HIMAC, and confirmed the recovery of leakage current and collected21 charge from radiation damage with heat annealing. To investigate higher radiation tolerance of22 the CIGS semiconductor, we irradiated CIGS solar cells with a 70 MeV proton beam with a non23 ionizing energy loss (NIEL) for 1016neq ·MeV/cm2 at the RARiS. The VIn and InCu defects created 24 by 70 MeV proton irradiation were observed by deep level transient spectroscopy (DLTS). During 25 thermal annealing at around 100◦C, the Cu+ and VCu− ions are excited to react with defects. These 26 ions interact with VIn and InCu defects, creating electrical neutrality : 2Cu+ + V2In− → Cu2VIn and 27 2VIn− + InCu2+ → 2VInInCu. By these reaction process, it is confirmed that both VIn and InCu defects 28 were reduced by the thermal annealing at 130◦C for two hours.29 Contents30 1 Introduction 131 2 Particle detector with CIGS semiconductor 132 2.1 CIGS detector performance study with 132Xe54+ beam at the HIMAC 233 3 70 MeV proton irradiation experiment at the RARiS 234 3.1 Defect levels measurement with DLTS method 435 4 Conclusion 436 1 Introduction37 A Cu(In, Ga)Se2 (CIGS) is an alloy semiconductor of CuInSe2 and CuGaSe2. Since the CIGS is a 38 direct band gap semiconductor, it has a high light absorption coefficient among solar cell materials39 and can absorb a broad spectrum of wavelengths, including in the infrared region. Therefore, 40 the solar cell with thin CIGS layer (∼ 2 𝜇m) has achieved a high energy conversion efficiency 41 (𝜂 ∼ 20%), comparable to silicon solar cells [1]. Japan Aerospace Exploration Agency (JAXA) 42 performed ground radiation test using 3 MeV a proton beam with a fluence of 3.0 ×1016cm−2, 43 and 1 MeV electron beam with a fluence of 3.0 ×1014cm−2, respectively [2]. The short-circuit 44 current ISC and open-circuit voltage (VOC) of CIGS solar cells degraded to 85% for ISC and 55% 45 for VOC after proton irradiation. However, the ISC of CIGS solar cells was recovered by the thermal 46 annealing in the dark condition at 400 K. Since the CIGS semiconductor has a lightweight and high 47 radiation tolerance, the CIGS solar cell is a promising candidate for space thin-film solar cells.48 In the high energy collider experiment such as High-Luminosity Large Hadron Collider ( HL-LHC),49 particledetectorsrequireradiationtoleranceofnon-ionizingenergyloss(NIEL)for1016 neqMeV/cm250 and total ionizing dose (TID) for 10 MGy. In this study, we have developed a particle detector51 with CIGS and evaluated high radiation tolerance of CIGS semiconductor by proton irradiation 52 experiment at the RARiS.53 2 Particle detector with CIGS semiconductor54 We have developed the CIGS detector shown in Fig. 1. The CIGS sensor is constructed based on a55 pn-junction consisting of a p-type CIGS layer and an n-type ZnO layer. A back contact of Mo with 56 0.8 𝜇m thickness is deposited by DC magnetron sputtering on an soda-lime glass (SLG) substrate.57 An anode electrode and a cathode were directly bonded to an Al layer and the Mo layer with the 58 Au wires, respectively. A 2 𝜇m thick of CIGS layer was deposited onto a substrate by evaporation 59 method through a three-stage process at Advance Industrial Science and Technology (AIST) [3]. 60 The p-type CIGS layer has carrier density with 1014 cm−3 and achieves to full depletion at a negative 61 bias voltage of 2V. We conducted the heavy ion irradiation experiment at the Heavy Ion Medical 62 Accelerator in Chiba (HIMAC) for evaluating the CIGS detector performance.Figure 1. Left and Center) The design of 2 𝜇m-CIGS detector. Right) Signal from 132Xe54+ beam with a kinematic energy of 400 MeV/u.63 2.1 CIGS detector performance study with 132Xe54+ beam at the HIMAC64 The HIMAC is a heavy ion accelerator facility in Japan. A 132Xe54+ ion beam with a kinematic 65 energy of 400 MeV/u was employed. Figure 1 (right) presents the integrated ADC value derived66 from Xe ion signal. This marks the first observation of a single particle using CIGS detector [4]. To67 evaluate the radiation tolerance of the CIGS detector, it was continuously irradiated with a 132Xe54+ 68 beam delivering a total amount of 0.6 MGy of 132Xe54+ beam. Figure 2 shows the degradation in the 69 performance of the CIGS detector under 132Xe54+ ion beam irradiation. The collected charge from 70 Xe ion signals gradually decreased to 50% of its initial value after Xe ion beam irradiation with an 71 amount of 0.6 MGy, while the leakage current increased from a few nA to 30 nA. After the xenon 72 ion beam irradiation, we treated thermal annealing on the CIGS detector for two hours at 130 ◦C. 73 As a result, both collected charge and leakage current recovered to levels comparable to these of74 the initial value. Therefore, the CIGS detector can maintain high performance through thermal75 annealing even after exposure to 0.6 MGy radiation damage. For the future collider experiment, a 76 particle detector is required higher radiation tolerance up to a fluence of 1017neqMeV/cm2 and a 77 dose of 10 MGy. In this study, we evaluated the high radiation tolerance of the CIGS semiconductor 78 using a 70 MeV proton beam at the RARiS in Japan.79 3 70 MeV proton irradiation experiment at the RARiS80 The Research Center for Accelerator and Radioisotope Science (RARiS) has a cyclotron accelerator81 facility at Tohoku University in Japan. We irradiated CIGS solar cells with a proton beam,82 accelerated to an energy of 70 MeV by the RARiS facility, with a fluence of 7.5×1015 MeV · neq/cm283 and with a dose of 4.1 MGy at -15 ◦C using a cold dry-nitrogen gas flow. To evaluate the radiation 84 tolerance of CIGS solar cells, We measured the short-circuit current density (JSC) of the CIGS 85 samples under an AM1.5 spectrum, with 1-sun simulated light illumination at room temperature 86 [3]. Figure 3 (left) shows the annealing time dependence of the relative ratio of the short-circuit 87 current density (JSC). After proton irradiation, the JSC degraded to about half of its initial value. 88 However, the thermal annealing at around 100◦C in dark condition allowed the recovery of defects 89 induced by 70 MeV proton irradiation. A certain ion may become activated during heating. The90 activated ion is expected to react and contribute to recovery process. In this model, the activationFigure 2. Left) A relative ratio of collected charge to that before irradiation during 132Xe54+ ion irradiation with a TID of 0.6 MGy. The purple regions indicate the annealing period at 130 ◦C. Right) A leakage current during 132Xe54+ ion irradiation with a TID of 0.6 MGy.91 energy (Ea) during thermal annealing can be described using Arrhenius equation as follows:−Ea k = Aexp  , (3.1) kbt92 where A is a constant factor, kbt is the Boltzmann constant, and k is the reaction rate constant, which 93 depends on temperature (𝑇). In this study, the reaction rate constant (k) is evaluated through the 94 current density-voltage (J-V) characteristic under irradiating the sunlight with an AM1.5 spectrum 95 with 100 mW/cm2 at 25 ◦C. As a result of Arrhenius plot fitting shown in right figure of Fig. 3 96 (right), an excited energy during thermal annealing is obtained as 1.07 eV.97 From the first-principles analysis in Ref. [5], copper ions (Cu+) and copper vacancies (VCu− ) are 98 activated during the thermal annealing at around 100 ◦C, and mainly contribute to recovery from 99 defects. In order to investigate the defects generated by 70 MeV proton irradiation, we conducted 100 the deep level transient spectroscopy (DLTS).Figure 3. Left) Annealing time dependence of JSC at 90, 110 and 130◦C. Right) The fitting result with Arrhenius equation. Each reaction rate constant (k) is estimatad by recovery speed in JSC value (shown in left figure).101 3.1 Defect levels measurement with DLTS method102 The DLTS method is a powerful experimental technique used to investigate charge carrier traps in103 semiconductors. In this study, the DLTS measurement were performed using the SemiLab DLS-104 83D instrument. The target temperature was controlled by an automatic liquid nitrogen cryostat,105 which covered a temperature range from 77K to 400 K. Figure 4 (left) shows the DLTS signal 106 observed through integrated capacitance transients after an injection pulse from -5V to zero-bias.107 As results of DLTS measurements, two clear peaks that did not appear before irradiation, were 108 observed after proton irradiation. Moreover, both defects decreased by the thermal annealing at 130◦109 C for one hour. In the p-type semiconductor layer such as CIGS, a positive and a negative peaks 110 indicate an acceptor and a donor defect levels, respectively. These defect levels (𝐸𝑔) and capture 111 cross section (sigma) follow the Arrhenius equation as en,p Egln( ) = ln(K𝜎) −  (3.2) T2 kbtT112 The K is a constant depending on the effective mass of the semiconductor, and the kbt is the113 Boltzmannconstant. Theelectronorholethermalemissionratefromadeepstate, en,p, isdetermined114 by the injection frequency where f = en,p/2.17 in the SemiLab DLS-83D instrument. Figure 4115 (right) shows the Arrhenius plots of defect peaks from the CIGS solar cells. The energy level of the116 negative peak is 0.55 eV below the conduction band, while that of the positive peak is 0.44 eV above 117 valence band. According to first-principles calculations in CIS crystals, the negative and positive 118 peaks in Fig. 4 correspond to InCu and VIn defects, respectively.119 In Ref. [6], a copper vacancy (VCu) and InCu defects were observed in the CIGS solar cells with120 admittance spectroscopy (AS) method after 0.38 MeV proton irradiation. On the other hand, our 121 DLTS instrument did not have sensitivity to detect the VCu defect because this defect is expected to 122 appear in a lower temperature region (< 77K). However, we observed the VIn defect, which is not 123 reported in Ref. [6].124 The reduction of both VIn and InCu defects was observed during thermal annealing at around 100◦C. 125 ThisresultindicatesthatactivatingionsofCu+ andVCu− reactwiththeVIn andInCu defectsandcreate 126 an electrical neutrality reaction: 2Cu++V2In− → Cu2VIn and 2VIn− +In2Cu+ → 2VInInCu. The electrical 127 neutrality states prevent carrier trapping and facilitates recovery of semiconductor performances.128 This recovery process is also effective in the CIGS detector because the recovery of leakage current 129 and collected charge from radiation damage were observed in the HIMAC experiment.130 4 Conclusion131 We investigated the radiation tolerance of the CIGS semiconductor by 70 MeV proton irradiation 132 with a fluence of 7.5×1015 MeV·neq/cm2. The short-circuit current density (JSC) during 1-sunlight 133 injection was decreased to half of its initial value after proton irradiation, but it was recovered to 134 85% with two-hour thermal annealing at 130◦C. Therefore, it is clear that the CIGS semiconductor 135 exhibits the high radiation tolerance with a fluence of 7.5 × 1015MeV · neq/cm2. We identified two 136 defect, VIn and InCu, created by 70 MeV proton irradiation using the DLTS method. This study 137 demonstrates that the CIGS detector has a potential to tolerant higher radiation level expected in 138 the future collider experiment (1017MeV · neq/cm2).Figure 4. Left) DLTS signal plots, before irradiation (black plot), after irradiation (red plot) and after one hour heating at 130◦C (blue plot). Right) Fitting result of Arrhenius plots. The accepter trap (red line) indicates VIn defect with defect level of 0.55 eV, and the donor trap (blue line) shows InCu defect with defect level of 0.44 eV.139 Acknowledgments140 This work was supported by World Premier International Research Center Initiative (WPI), the141 Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. This work was142 also supported by JSPS KAKENHI Grant No. 21K18635, 23H01191 and 23K25887 from MEXT,143 Japan and the Tsukuba Innovation Area (TIA). We appreciate the support provided for the Research144 Project with Heavy Ions at NIRS-HIMAC (Program No. 21H455) that contributed to part of145 this study. We also thank the Research Center for Accelerator and Radioisotope Science, Tohoku 146 University, for providing us with the proton beam used in this study.147 References148 [1] S. Niki et al., "CIGS absorbers and processes", Prog. Photovolt. Res. Appl. 18 (2010) 453-466, 149 https://doi.org/10.1002/pip.969.150 [2] M. Imaizumi et al., "Activity and Current Status of R&D on Space Solar Cells in Japan", Prog.151 Photovolt. Res. Appl. 13 (2005) 529–543.152 [3] J. Nishinaga et al., "Annealing effects on Cu(In, Ga)Se2 solar cells irradiated by high-fluence proton 153 beam", Jpn. J. Appl. Phys. 62 (2023) SK1014, https://doi.org/10.35848/1347-4065/acc53b.154 [4] M. Togawa et al., "The CIGS semiconductor detector for particle physics", JINST 19 (2024) C05042, 155 https://doi.org/10.1088/1748-0221/19/05/C05042.156 [5] S. Nakamura et al., "First-Principles Study of Diffusion of Cu and In Atoms in CuInSe2",Jpn. J. Appl.157 Phys. 52 (2013) 04CR01, http://dx.doi.org/10.7567/JJAP.52.04CR01.158 [6] S. Kawakita et al., "Analysis of Anomalous Degradation of CuInSe2 Thin-Filim Solar Cells Irradiated 159 with Protons",Jpn. J. Appl. Phys. 46 (2007) L670, https://doi.org/10.1143/JJAP.46.L670.– 2 –– 2 –image0.jpgimage10.jpgimage20.jpgimage4.jpgimage5.jpgimage30.jpgimage40.jpgimage6.pngimage7.jpgimage8.jpgimage6.jpgimage70.jpgimage1.jpgimage2.jpgimage3.jpg