Radiation hardness and conduction mechanisms of MINP solar cells on Ga- and B-doped Si substrates

Metal-insulator-n+Si-p+Si solar cells, fabricated on Ga- and B-doped substrates, were compared for tolerance to 1.0-MeV electron irradiation. Cells were tested by deep-level transient spectroscopy and current spectroscopic techniques prior to and after irradiation. Ga-doped substrates produced cells with superior tolerance to irradiation. After irradiation, B-doped cells gave defect levels more towards the upper half of the bandgap compared to Ga-doped cells, which showed levels toward the lower half. After irradiation, B-doped cells appear to be more susceptible to S-R-H recombination, whereas Ga-doped cells exhibit a multistep tunneling recombination. The latter results in a smaller reverse saturation current which better preserves Voc.