Characteristic of Displacement Defects in n-p-n Transistors Caused by Various Heavy Ion Irradiations

Characteristics of displacement defects in n-p-n bipolar junction transistors (BJTs) caused by heavy ions with various nonionizing energy loss (NIEL) values are studied in this paper. The key electrical parameters are measured in situ during irradiation. Behavior of the radiation-induced defects is characterized by deep level transient spectroscopy (DLTS) after the irradiation and the post irradiation annealing. Experimental results indicate that at a given displacement damage dose, the excess base current shows two ideality factors, which are close to 2 for small VEB and close to 1 for large VEB, respectively. Moreover, the two ideality factors do not change with the increasing irradiation fluence. These results indicate that heavy ion irradiations mainly produce displacement damage on the BJTs. With increasing displacement damage dose, the change in the reciprocal of current gain caused by 10-40 MeV Si and 25 MeV O ions can be normalized in one line, which shows the displacement damage is independent of the NIEL value. Based on the DLTS analysis and isochronal annealing, at a given displacement damage dose, the characteristic of displacement defects caused by 40 MeV Si, 10 MeV Si, and 25 MeV O ion irradiations is different. Heavy ions with low NIEL value primarily generate isolated defects in the BJTs, while heavy ions with high NIEL value mainly produce clustered defects. Therefore, we conclude that although the displacement defects caused by heavy ions with various NIEL are different, the degradation of the electrical property of the BJTs is independent of NIEL.