Performance degradation of InGaP and GaAs cell by radiation of electron beams at 70 keV

Space solar cells are utilized as an electric power source such as a satellite, studied about degradation with radiation. 3-junction solar cells (3J) using a III-V compound semiconductor current is used, InGaP solar cells which is the top cell has a highest radiation resistance in 3J. To clarify the cause of this high radiation resistance, the mechanism of the radiation degradation in InGaP cells is investigated. In the previous study, InGaP cells was found to be degraded by irradiation with the electron beam at relatively low energies which are not able to induce the recoil of atoms in the cells. In order to understand the mechanism of the degradation, the samples of InGaP cells were irradiated with electron beams in vacuum under cooling with ice by using a Cockcroft-Walton type accelerator at Osaka Prefecture University. The energies and the fluences of the electron beams for irradiation were 70 keV and from 1x10¹⁴ to 3x10¹⁶ cm^-2, respectively. For comparison, it was also irradiated to GaAs solar cells. The measurements of light-current-voltage (LIV), electroluminescence (EL) and capacitance-voltage were carried out for the samples. After the irradiation the open-circuit voltage, the intensity of EL in InGaP cells were decreased. On the other hand, the carrier concentration is increased. The LIV characteristics of GaAs cells was degraded less than InGaP cells. (author)