Effects of impurities on generation of radiation-induced defects in Si single crystals and space solar cells

Anomalous degradation of Si space solar cells for the ETS-VI satellite suggests the importance of understanding the origins of radiation-induced defects in Si, because such defects are responsible for carrier removal, type conversion and reduction in minority-carrier lifetime. Effects of impurities on generation of radiation-induced defects in Si have been studied using measurements of DLTS and minority-carrier lifetime. Boron concentration [Bs]1/2 and oxygen concentration [Oi]1/8 dependences of damage coefficient for minority-carrier lifetime suggest that is Ci-Oi defect is more responsible for minority-carrier lifetime degradation in the low [Bs] and boron-related defect such as Bi-Bs or Bi-Oi-X and Ev+0.48 eV defect is more responsible in the high [Bs]. Effectiveness of Ga impurity for reducing carrier removal effect with irradiation compared to B impurity is also found.