Effects of Impurities on Gamma-Irradiated Silicon Crystal Examined by Photovoltaic Effect ofP-NJunction Diode

Minority carrier lifetime in 60 Co gamma-irradiated silicon bulk crystals is examined by photovoltaic effect of silicon p - n junction, and following results are disclosed. 1) Damage constant, K, increases with impurity concentration of bulk crystals. K is smaller in p -type crystals than in n -type. 2) For isochronal annealing, recovery stages of n -type bulk crystals at 100–150°C and 300°C are found. In p -type crystals, reverse annealing is observed at 200–300°C. 3) From the temperature dependence of carrier lifetime, energy levels of the recombination centers at E c -0.42 for n -type and E v +0.32, E v +0.25 eV for p -type crystals are found. 4) Recovery stage of p -type bulk crystals due to gamma irradiation at 81 K is observed at about 150 K, but that of n -type is not observed between 80 and 300 K. 5) The lifetime degradation in p -type crystals due to gamma irradiation at 81 K is reduced when minority carrier is injected after the irradiation.