1MeV electron irradiation effects of GaAs/Si solar cells
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1MeV electron irradiation effects of GaAs/Si solar cells N. Chandrasekaran, T. Soga, Y. Inuzuka, M. Imaizumi 1, H. Taguchi and T. Jimbo. Department of Environmental Technology and Urban Planning, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan. 1 Japan Aerospace Exploration Agency, Tsukuba, 305-8505, Japan. ABSTRACT The characteristics of 1 MeV electron irradiated GaAs solar cells grown on GaAs and Si substrates are studied under dark and AM 0 conditions. The short circuit currents (Isc) for GaAs/GaAs cell and GaAs/Si cell have been decreased at higher fluences. The degradation rate of Voc and Pmax for GaAs/Si is slower than that of GaAs/GaAs at the fluence 1x1016 cm-2. This is due to the high radiation resistance of saturation current. It has been due to slow generation of arsnic vacancies related defect (VAs) in the GaAs/Si solar cell, which is determined by photoluminescence analyses and deep level transient spectroscopy. INTRODUCTION GaAs solar cell has excellent conversion efficiency and good radiation tolerance behavior in radiation environment, so it can be widely used as power generation device in the space applications [1]. In order to reduce the weight, cost effect and to improve the radiation tolerance, GaAs solar cell grown on alternative substrate such as Si [2] has been studied. Also the Si substrates are available in large area and good mechanical strength, which is highly suitable for space applications. But, the efficiency of the GaAs solar cells on Si substrate is inferior to that on GaAs substrate [3]. This inferiority is due to the difference in lattice constant mismatch and thermal expansion coefficient between GaAs and Si. In the space applications, the end-of-life (EOL) efficiency is more important than that of beginning-of- life (BOL) efficiency of the solar cell. A realized report shows that GaAs solar cell on Si substrate was less degraded when compared to that on GaAs substrate [4]. However, till now the degradation mechanisms of GaAs solar cell on Si substrate are not clearly understood because of the insufficient study. There are a few reports on the electron irradiation effects of GaAs solar cell on Si substrates[5]. The 1 MeV electrons have been frequently used to study the defects in a semiconductor. The effects of highenergy electron irradiation on n-GaAs have been the subjects of large number of works [6,7]. Electron irradiation generally produces point defect in semiconductor because of their recoil energy. After electron irradiation in GaAs, the direct formation of anti-sites is clearly explained[8]. In the present study, the high-energy electron (1MeV) irradiation effects on GaAs solar cells and GaAs layer grown by metal organic chemical vapor deposition (MOCVD) on Si substrate and compared with those on GaAs substrate. Electrical characterizations of these samples were carried out deep level defects by deep level transient spectroscopy (DLTS). The optical properties of the samples are studied by photoluminescence (PL) spectroscopy. EXPERIMENT
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