The Effect of Ionizing Radiations on the Structural, Electrical and Optical Properties of AIIBVI Polycrystalline Thin Fi
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1012-Y12-01
The Effect of Ionizing Radiations on the Structural, Electrical and Optical Properties of AIIBVI Polycrystalline Thin Films Used as Solar Cell Materials Lucian Ion1, Vlad Andrei Antohe1, Marian Ghenescu1, Oana Ghenescu1, Rosemary Bazavan1, Mihai Danila2, Marius Marin Gugiu3, and Stefan Antohe1 1 Faculty of Physics, University of Bucharest, 405 Atomistilor, Magurele-Ilfov, 077125, Romania 2 National Institute of Research and Development in Microtechnologies, 126A, Erou Iancu Nicolae street, Bucharest, 077190, Romania 3 Horia Hulubei National Institute of Physics and Nuclear Engineering, 407 Atomistilor, Magurele-Ilfov, 077125, Romania ABSTRACT The effects of irradiation with high-energy protons (3 MeV, up to a fluency of 1013 protons/cm2), on structural, electrical and optical properties of polycrystalline CdS and CdTe thin films have been investigated. XRD investigation has revealed that the films contain wurtzite-type CdS, (001) preferentially oriented in the growth direction, and cubic phase CdTe, respectively. The defects induced by ionizing radiations have been studied by thermally stimulated current spectroscopy (TSC). Eight kinds of traps were observed in the CdS films and their energies, densities and capture cross sections were quantified. INTRODUCTION AIIBVI compounds with cadmium are good candidates for optoelectronic applications (optical detectors, solar cells). For instance, CdS/CdTe heterostructures have been extensively studied [1-3] because of their promising photovoltaic conversion efficiency. Since the performance of the devices based on thin film technology strongly depends on physical properties of the films, it is important to identify and, if possible, to control the defects having the most important influence on electrical and/or optical properties of the films. Electrical properties of thin films of CdS and CdTe were investigated by many researchers [4-7]. However, studies on the influence of the ionizing radiations on their physical properties are rather scarce [8-11]. The importance of such a study is justified by the potential use of thin films of AIIBVI compounds, especially CdS and CdTe, for producing solar cells for space technology applications, where the flux of ionizing radiations is high. In this paper we report on the changes induced by high energy proton irradiation (3 MeV, fluencies of 3◊1013 protons/cm2) on the electrical properties of CdS and CdTe thin polycrystalline films, using thermally stimulated current (TSC) measurements. The TSC method has been used elsewhere for that purpose and different procedures were proposed [11-14]. EXPERIMENTAL CdS and CdTe films were deposited on glass substrates (Sigma Chemicals S-8400), using thermal-vacuum evaporation from CdS and CdTe powder, respectively. CdTe powder was vacuum sublimated at a pressure of 5◊10-5 Torr from a quartz container heated to 650 ∫C, the substrate being maintained at 250 ∫C. In the case of CdS, the container was heated to 1100 ∫C. The substrate temperature was maintained at 220 ∫C during deposition. To
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