Lifetime in Neutron Irradiated Silicon - Application to Devices

Detailed measurements on special gated Si p+n diodes yield the damage parameters associated with the three basic current components in p-n junctions. Recombination in the neutral bulk, recombination and generation in the space-charge region, and recombination and generation at the surface are characterized over a wide range of neutron doses and injection levels. For recombination in the neutral bulk, the lifetime damage constant is about 3 x 105 n-sec/cm2 at high injection levels and varies with dose between 103 and 104 n-sec/cm2 for low injection levels. The damage constant for the space-charge region recombination lifetime is about 5 x 105 n-sec/cm2 for forward biases in the range of 0.1 to 0.3 V and the damage constant for the generation lifetime in the space-charge region is 5 x 107 n-sec/cm2 both nearly independent of dose. The surface generation and recombination velocities are process dependent and are not a linear function of the dose. The surface generation velocity increases from about 10 cm/sec at 2 x 1011 n/cm2 to saturate at about 100 cm/sec at 1014 n/cm2 in the diodes studied here. Using these data, the grounded emitter current gain (hFE) for a Si pnp transistor (2N4872) is predicted as a function of dose and current density. Both the dose and the current density dependence of hFE, as predicted by our V-I characteristics and deduced lifetimes, are in reasonable agreement with the published specifications.