A Direct Evidence of the Annealing Effect of Ionization Damage on Displacement Damage in NPN Transistors

In this paper, based on the sequential irradiation of 40 MeV Si ions and Co-60 gamma ray, a direct evidence of the annealing effect of ionization damage on displacement damage in 2N2219 NPN bipolar junction transistors (BJTs) is investigated. Electrical parameters are measured using KEITHLEY 4200-SCS semiconductor characterization system during irradiation. The radiation induced defects are characterized by deep level transient spectroscopy (DLTS). The experimental results show that the degradation of current gain for the F2N2219 BJTs for the sum of the independent Co-60 gamma radiation and heavy ion irradiation is larger than that for the sequential irradiations, indicating the existence of significant synergistic effect. For lower fluence of 40 MeV Si ions, when the dose of Co-60 gamma ray is lower, the excess base current of the irradiated transistors by the sequential irradiation is less than one of the irradiated transistors by the independent 40 MeV Si ions. When fluence of 40 MeV Si ions is more than 6×l08/cm2, all the excess base current of the irradiated transistors by the sequential irradiation is less than one of the irradiated transistors by the independent 40 MeV Si ions. These results show that ionization damage on the transistors caused by the subsequent Co-60 gamma ray has an annealing effect on displacement damage caused by the 40 MeV Si ions. DLTS analyses show that the displacement defects especially in V2(-/0) centers caused by the 40 MeV Si ions are annealed due to the oxide charges induced by Co-60 gamma ray irradiations. Moreover, the fluence of the independent 40 MeV Si ions is the larger, the annealing effect of the displacement defects is the more obvious.