HIGH AND LOW-ENERGY PROTON RADIATION-DAMAGE IN P N INP MOCVD SOLAR-CELLS/

Indium phosphide p(+)/n/n(+) solar cells, fabricated by metal organic chemical vapor deposition, were irradiated with 0.2-MeV and 10-MeV pro tons to a fluence of 10(13) cm(-2). The power output degradation, I-V behavior, carrier concentration and defect concentration were observed at intermediate points throughout the irradiations. The 0.2-MeV proto n-irradiated solar cells suffered much greater and more rapid degradat ion in power output than those irradiated with 10 MeV protons. The eff iciency losses were accompanied by larger increases in the recombinati on currents in the 0.2-MeV proton-irradiated solar cells. The low-ener gy proton irradiations also had a larger impact on the series resistan ce of the solar cells. Despite the radiation-induced damage, the carri er concentration in the base of the solar cells showed no reduction af ter 10-MeV or 0.2-MeV proton irradiations and even increased during ir radiation with 0.2-MeV protons. In a deep-level transient spectroscopy study of the irradiated samples, the minority carrier defects H4 and H5 at E(v) + 0.33 and E(v) + 0.52 eV and the majority carrier defects E7 and E10 at E(c) - 0.39 and E(c) - 0.74 eV were observed. The defect introduction rates for the 0.2-MeV proton irradiations were about 20 times higher than for the 10-MeV proton irradiations. The defect E10, observed here after irradiation, has been shown to act as a donor in i rradiated n-type InP and may be responsible for obscuring carrier remo val. The results of this study ave consistent with the much greater da mage produced by low-energy protons whose limited range causes them to stop in the active region of the solar cell.