The effect of neutron irradiation on silicon photodiodes

Neutron radiation testing was performed on a total of 125 silicon photodiodes to investigate the changes in the device parameters after neutron exposure. A californium-252 source was used to irradiate the photodiodes with 1-MeV equivalent neutrons having fluences in the range of 5×10¹¹ to 10¹⁴ n/cm². The photodiode forward voltage drop, ideality factor, and series resistance increased after neutron exposure. The increased series resistance caused a degradation in diode photocurrent linearity. An empirical expression for post-neutron-irradiation changes in photodiode linearity is presented. Neutron-induced changes in the photodiode shunt resistance and dark current were modeled using simple expressions that allow device designers to estimate changes in photocurrent linearity, shunt resistance, and dark current after neutron exposure. No postirradiation change in the ultraviolet quantum efficiency of diodes without recombination in the front region was observed. This suggests that neutron irradiation does not affect the Si-SiO₂ interface recombination velocity of p-n junction diodes