Anomalous Damage Mechanism in PNP Silicon Transistors Due to Thermal Neutrons

Very low energy neutrons (E < 1 eV) were found to produce damage to pnp silicon transistors comparable to that produced by fast neutrons (E > 10 keV). The effectiveness of thermal neutrons was quite varied; ratios of thermal-to-fast neutron damage constants from less than 10-3 to nearly unity were obtained. The damage mechanism was tentatively identified to be the result of a [B10 (n, α) Li7] reaction in the emitter region of the device whereby energetic alpha and Li particles are emitted and subsequently produce damage in the base region of the device. The role of the lithium recoil was identified to be responsible for the large observed damage ratios; however, even larger ratios are possible for certain types of devices.