Implications of radiation-induced dopant deactivation for npn bipolar junction transistors

Metal-oxide-silicon capacitors fabricated in a bipolar process were examine d for densities of oxide trapped charge, interface traps and deactivated su bstrate accepters following high-dose-rate irradiation at 100 degreesC. Acc epter neutralization near the Si surface occurs most efficiently for small irradiation biases in depletion. The bias dependence is consistent with com pensation and passivation mechanisms involving the drift of H+ ions in the oxide and Si layers and the availability of holes in the Si depletion regio n. The capacitor data were used to simulate the impact of accepter neutrali zation on the current gain of an irradiated npn bipolar transistor Neutrali zed accepters near the base surface enhance current gain degradation associ ated with radiation-induced oxide trapped charge and interface traps by inc reasing base recombination, The additional recombination results from the c onvergence of carrier concentrations in the base and increased sensitivity of the base to oxide trapped charge. The enhanced gain degradation is moder ated by increased electron injection from the emitter These results suggest that accepter neutralization may complicate hardness assurance test method s for linear circuits, which are based on elevated temperature irradiations .