Analysis of structure change of Si solar cells irradiated with high fluence electrons

An anomalous increase in short-circuit current of Si space solar cells, fol lowed by an abrupt decrease and cell failure has been induced by fluences g reater than 10(16) cm(-2) of 1 MeV electrons. This can be explained by a re duction in carrier concentration of the base region, in addition to a decre ase of minority-carrier diffusion length. A change in the spectral response has been observed along the change in the short-circuit current. The spect ral response has been modeled to account for radiation-induced changes in t he cell structure. The results show that the junction depth increases when the degradation occurs. Also, spectral response after cell failure has been explained by conduction-type conversion of the base layer. This conversion is confirmed by a cross-sectional electron-beam-induced current signal. A mechanism for these phenomena has been proposed, which consists of the gene ration of vacancies and the vacancy-mediated diffusion of phosphorous. (C) 1999 American Institute of Physics. [S0021-8979(99)06303-3].