Anomalous dose rate effects in gamma irradiated SiGe heterojunction bipolar transistors

Low dose rate (LDR) cobalt-60 (0.1 rad(Si)/s) gamma irradiated Silicon Germ anium (SiGe) Heterojunction Bipolar Transistors (HBTs) were studied. Compar isons were made with devices irradiated with 300 rad(Si)/s gamma radiation to verify if LDR radiation is a serious radiation hardness assurance (RHA) issue. Almost no LDR, degradation was observed in this technology up to 50 krad(Si). The assumption of the presence of two competing mechanisms is jus tified by experimental results. At low total dose (less than or equal to 20 krad), an anomalous base current decrease was observed which is attributed to self-annealing of deep-level traps to shallower levels. An increase in base current at larger total doses is attributed to radiation induced gener ation-recombination (G/R) center generation. Experiments on gate-assisted l ateral PNP transistors and 2D numerical simulations using MEDICI were used to confirm these assertions.