Research on the Combined Effects of Ionization and Displacement Defects in NPN Transistors Based on Deep Level Transient Spectroscopy

The properties of the combined effect between ionization and displacement defects have been researched on the base-collector junctions of 3DG110 silicon NPN bipolar junction transistors (BJTs) irradiated by 6 MeV carbon (C) ions with different fluence. The Gummel curve is used to characterize the degradation of the current gain at a given fluence. Nonlinear relationship, induced by 6 MeV C ions with lower fluence, between irradiation fluence and BJT radiation response can be observed, which is attributed to the combined effect. Evolution of deep level centers is characterized by the deep level transient spectroscopy (DLTS) with various biases. An unusual discovery is that the deep level centers decrease in the amplitude of DLTS peaks with increasing the biases. Based on the results of DLTS measurement, interface traps caused by 6 MeV C ions produce apparent enhanced effect to displacement defects in the base-collector junction of NPN BJT. Meanwhile, two factors, including bias used in DLTS measurement and irradiation fluence, can influence characteristics of DLTS signals caused by oxide-trapped charge. With increasing the bias or the irradiation fluence, both the height and the temperature of the defect peaks induced by the oxide charge in DLTS spectra will increase, illustrating concentration and energy level of the defects are enhanced.