Displacement Damage in Silicon and Germanium Transistors

An experimental and theoretical analysis of neutron damage to germanium and silicon transistors is presented. A combination of experimental data and first order theory has been used to determine lifetime damage constant as a function of neutron energy. Two separate effects attributable to the recombination centers have been identified. At low bias levels recombination centers present in the emitter diode field region cause a very large decrease in current gain. At higher levels of emitter bias current recombination centers present in the base region cause a reduction in current gain. The temperature dependence of current gain is stronger when emitter region recombination is the dominant process than when base region recombination is most effective. The damage thresholds of silicon transistors can be increased by operating at high ambient temperatures. The characteristics of the recombination centers have been determined from the experimental data and agree well with values previously obtained by measurements on bulk semiconductor samples. Two discrete recombination levels in silicon and two discrete recombination levels in germanium are shown to determine the dependence of transistor current gain on neutron radiation.