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1 Chapter No.: 16 Date: Time: 3:48 pm Page: 1/8 1 Chapter 16 2 I V Characterization of the Irradiated 3 ZnO:Al Thin Film on P-Si Wafers By 4 Reactor Neutrons 5 Emrah Gunaydın, Utku Canci Matur, Nilgun Baydogan, 6 A. Beril Tugrul, Huseyin Cimenoglu and Serco Serkis Yesilkaya Abstract ZnO:Al/p-Si heterojunctions were fabricated by solgel dip coating 10 technique onto p-type Si wafer substrates. Al-doped zinc oxide (ZnO:Al) thin film 11 on p-si wafer was irradiated by reactor neutrons at ITU TRIGA Mark-II nuclear 12 reactor. Neutron irradiation was performed with neutron/gamma ratio at (n cm 2 s 1 mr 1 ). The effect of neutron irradiation on the electrical characteristics 14 of the ZnO:Al thin film was evaluated by means of current voltage (I V) charac- 15 teristics for the unirradiated and the irradiated states. For this purpose, the changes 16 of I V characteristics of the unirradiated ZnO:Al thin films were compared with the 17 irradiated ZnO:Al by reactor neutrons. The irradiated thin ZnO:Al film cell structure 18 is appropriate for the usage of solar cell material which is promising energy 19 material. 20 E. Gunaydın (&) N. Baydogan A.B. Tugrul H. Cimenoglu Istanbul Technical University, Istanbul, Turkey egunaydin@itu.edu.tr N. Baydogan dogannil@itu.edu.tr A.B. Tugrul beril@itu.edu.tr H. Cimenoglu cimenogluh@itu.edu.tr U.C. Matur Gedik University, Istanbul, Turkey utku.canci@gedik.edu.tr S.S. Yesilkaya Yildiz Technical University, Istanbul, Turkey serkaya@yildiz.edu.tr Springer International Publishing Switzerland 2015 A.N. Bilge et al. (eds.), Energy Systems and Management, Springer Proceedings in Energy, DOI / _16 1

2 Chapter No.: 16 Date: Time: 3:48 pm Page: 2/8 2 E. Gunaydın et al Introduction 22 Photovoltaic (PV) refers to the conversion of light energy into electricity using 23 electronic devices called solar cells. In developing next-generation solar alternatives, 24 a thinner profile is paramount. The majority of solar cells in existence today are made 25 from rigid multi- or single-crystalline silicon (Si) wafers. Typically 150 µm thick, 26 the wafers demand multiple processing steps before they can be integrated into a 27 module. On the contrary, thin-film solar cells utilize only a 1- to 4-µm-thick layer of 28 semiconducting material to produce electricity, thus requiring less processing and 29 fewer materials. These cost-saving alternatives also offer another important advan- 30 tage as compared to wafer-based modules in that they can be used in a wide range of 31 applications. Thin-film solar cells employ light weight and making them ideal for 32 advanced applications such as building-integrated PV ( 33 solutions-technology/thin-film-photovoltaics/). The ZnO coating as conducting 34 electrode makes the device as the reliable energy source for the use in transparent 35 energy applications. The conducting electrodes consisting of ZnO:Al thin films have 36 several favorable properties, including good transparency, high electron mobility, 37 wide bandgap, and strong room-temperature luminescence. Hence, these properties 38 of ZnO:Al thin films are used in the emerging applications for transparent electrodes 39 in energy-saving or heat-protecting windows, in liquid crystal displays, and in 40 electronics as thin-film transistors and light-emitting diodes. ZnO:Al/p-Si hetero- 41 junctions can be used to obtain clean, abundant, and convenient energy. The 42 researches on ZnO:Al/p-Si heterojunctions attracts an increasing attention for the use 43 of ZnO:Al/p-Si heterojunctions in solar cells as they have a number of advantages, 44 such as economic and simple processing steps and an excellent blue response. 45 ZnO structures are useful for space and terrestrial applications at strong particle 46 irradiation as ZnO is extremely radiation resistant to radiation damage with respect 47 to other semiconducting materials. High-energy particles can create the point 48 defects (i.e., vacancies and interstitials) with the changes of their optical and 49 electrical properties. Earlier studies have shown that ZnO compounds are fairly 50 resistant to harsh environments and displacement damage resulting from particle 51 irradiation (Ramirez et al. 2013). ZnO structures are useful for space and terrestrial 52 applications for which irradiation hardness is a prerequisite (Elliot 2005). Radiation 53 resistance makes ZnO a suitable candidate for space applications. Hence, ZnO thin 54 films are good candidates for transparent conductive oxide films at aggressive 55 radiation environment and this thin film is a good choice for electronic or opto- 56 electronic applications for the use in solar cells. Their property could be advanta- 57 geous for electronic and photonic applications in radiation environments (Coskun 58 et al. 2009). For space applications, nuclear researches, extraction uranium ores, 59 and their treatment, semiconducting devices have to operate in harsh radiation 60 conditions. An important point for such applications is the high radiation resistivity 61 of the semiconducting material, providing reliable operation of devices during 62 extended periods of time. AQ1 AQ2

3 Chapter No.: 16 Date: Time: 3:48 pm Page: 3/8 16 I V Characterization of the Irradiated ZnO:Al Thin Film 3 63 The effect of high-energy neutron irradiation has been reported for ZnO:Al in 64 this study. The effect of reactor neutrons on current voltage characteristics of ZnO is 65 not detailed regarding in literature. In particular, to our knowledge in the literature, 66 data pertaining to the changes of current voltage characteristics in the induced ZnO: 67 Al by neutrons are unknown at different Al concentrations. Hence, this study is 68 initiated to evaluate the neutron effect on ZnO:Al/p-Si heterojunctions. The appli- 69 cations of devices based on ZnO depend essentially on Al concentration and pro- 70 duction method. This problem is closely related to the interaction of ZnO with high- 71 energy particles such as neutrons. It leads to a generation of radiation defects in 72 ZnO crystal lattice similar to native defects at thermodynamic equilibrium and at 73 growing thin films by different methods. The types of defects generated by radia- 74 tion, the processes of their annealing, and the methods for their characterization are 75 considered. The impact of radiation on I V characteristics of ZnO:Al are compared 76 at different Al concentrations Experimental 78 ZnO:Al thin films deposited by solgel dip coating technique at four different Al 79 concentrations were annealed in vacuum ambient at 700 C. The details of the 80 production process of ZnO:Al thin films deposited by solgel dip coating technique 81 were given elsewhere (Baydogan et al. 2013). This paper presents some information 82 about the impact of neutron irradiation on the surface of ZnO:Al thin film. The 83 ZnO:Al thin films were irradiated in the tangential beam tube of the ITU TRIGA 84 Mark-II Training Reactor (Fig. 16.1). ITU TRIGA Mark-II Training Reactor Fig ITU TRIGA Mark-II reactor arrangement with port facility

4 Chapter No.: 16 Date: Time: 3:48 pm Page: 4/8 4 E. Gunaydın et al. 85 operates at a maximum power of 250 kw (Yavuz et al. 1993). The reactor was 86 operated at this maximum power during 3 h Results and Discussion 88 Phase analysis of the ZnO:Al thin films was made by qualitative X-ray diffraction 89 (XRD) using Cu-K α radiation. For this purpose, a GBC-MMA X-ray diffractometer 90 was operated at 35 kv and 28.5 ma with a constant scan rate of 2 /min. XRD 91 analyses were performed to scan the samples in a 2θ range between 30 and ZnO peaks from the (100), (002), (101), (110), and (103) planes were identified in 93 the XRD patterns in Fig The changes in electrical resistivity of ZnO:Al thin 94 film with the rise of irradiation time by using reactor neutrons were presented in 95 Fig The decrease in electrical resistivity on the surface of ZnO:Al thin film 96 was determined with the rise of irradiation time by using reactor neutrons in 97 Fig I V characteristics of ZnO:Al thin film were investigated for Cu/ZnO:Al/p-Si/Al 99 configuration. I V characteristics of ZnO:Al thin film annealed at 700 C in vac- 100 uum ambient are presented in Figs (at dark) and 16.5 (at light). The changes of 101 I V characteristics were determined with the rise of Al concentrations. Current 102 density voltage characteristics of unirradiated ZnO:Al/p-Si heterojunctions are 103 presented at different Al concentrations in Fig Besides, Current density 104 voltage characteristics of irradiated ZnO:Al/p-Si heterojunctions were examined by 105 using reactor neutrons and are shown in Fig For this purpose, irradiation 106 process has continued during 3 h. Fig X-ray diffraction patterns of the ZnO:Al films annealed in nitrogen ambient depends on Al concentration AQ3 AQ4

5 Chapter No.: 16 Date: Time: 3:48 pm Page: 5/8 16 I V Characterization of the Irradiated ZnO:Al Thin Film 5 Fig The changes in electrical resistivity of ZnO:Al thin film with the rise of irradiation time by using reactor neutrons Fig The changes in I V characteristics of ZnO:Al thin film in dark

6 Chapter No.: 16 Date: Time: 3:48 pm Page: 6/8 6 E. Gunaydın et al. Fig The changes in I V characteristics of ZnO:Al thin film in light Fig Current density voltage characteristics of unirradiated ZnO:Al/p-Si heterojunctions

7 Chapter No.: 16 Date: Time: 3:48 pm Page: 7/8 16 I V Characterization of the Irradiated ZnO:Al Thin Film 7 Fig Current density voltage characteristics of irradiated ZnO:Al/p-Si heterojunctions by reactor neutrons during 3 h Conclusions 108 In Cu/ZnO:Al/p-Si/Al configuration, ZnO:Al/p-Si heterojunctions were examined 109 to evaluate their space and terrestrial solar cell applications at strong neutron 110 irradiation depending on extremely radiation-resistant properties of ZnO structures. 111 In the results of the study, it concluded as below: 112 There was an improvement in the electrical properties of the ZnO:Al thin film 113 after the irradiation by reactor neutrons. 114 The enhancement of the electrical performance in ZnO:Al/p-Si heterojunctions 115 was determined for all of the Al concentration at Cu/ZnO:Al/p-Si/Al 116 configuration. 117 The decrease of electrical resistivity of ZnO:Al thin film deposited by solgel dip 118 coating technique was concluded to have the potential for use in electronic 119 devices. 120 Irradiated thin ZnO:Al film modules are special when compared to traditional 121 crystalline products. Therefore, it can be said that the irradiated thin ZnO:Al film 122 cell structure is appropriate for the usage of solar cell material. 123 References 124 Baydogan, N., Ozdemir, O., & Cimenoglu, H. (2013). The improvement in the electrical properties 125 of nanospherical ZnO: Al thin film exposed to irradiation using a Co-60 radioisotope. 126 Radiation Physics and Chemistry, 89, Coskun, C., Guney, H., Gur, E., & Tuzemen, S. (2009). Effective annealing of ZnO thin films 128 grown by electrochemical deposition technique. Turkish Journal of Physics, 33, Elliot, T. B. (2005). Focus on semiconductor research. NewYork: Nova. 130 Hacıyakupoglu, S., Erenturk, S. A., Karatepe, N., Tugrul, A. B., Baytas, A. F., Altınsoy, N., 131 Baydogan, N., Buyuk, B., & Demir, E. (2012). Remediation investigation of selenium in

8 Chapter No.: 16 Date: Time: 3:48 pm Page: 8/8 8 E. Gunaydın et al. 132 aqueous environment with using activated carbon. In I. Dincer, F. Kadioglu, & C. O Colpan 133 (Eds.), Global Conference on Global Warming-2012 (GCGW-12), 8 12 Conference 134 Proceedings, p. 940, İstanbul. 135 Ramirez, J., Israel, Y. V., Li, Y. V., Basantani, H., & Jackson, T. N. (2013). Effects of gamma-ray 136 irradiation and electrical stress on ZnO thin film transistors. Canada: IEEE. ISBN: / AQ5