Evolution of Activation Energy of Interface Traps in LPNP Transistors Characterized by Deep-Level Transient Spectroscopy

The emission of charge carriers from the interface traps as a function of irradiation dose and bias voltage is investigated in terms of Poole-Frenkel effect (PFE) used by deep-level transient spectroscopy (DLTS). The electrical properties in lateral PNP (LPNP) transistors caused by Co60 gamma-ray radiation are measured in situ during irradiation, showing that the interface traps give the main contribution to the excess base current of LPNP transistors. Based on the DLTS results, with increasing irradiation dose, the density of the charged positive interface traps at a given bias voltage increases. This causes an increase in the electric-field strength in the space-charge region and a decrease in the activation energy of interface traps and an increase in the emission rate of charge carriers from the interface traps, showing a similar feature to the classical PFE. However, the charge sign of the interface traps changes from negative to positive, which is different to the classical PFE, and thus displays a new mode of PFE. In order to confirm this conclusion, various bias conditions are employed during DLTS measurements. With decreasing the reverse bias, the electric-field strength increases, leading to an obvious decrease in activation energy of the interface traps and increase in emission rate of charge carriers. Moreover, the interface traps are shown to be uniformly located at the Si/SiO
₂
interface, and the uniformly distributed interface traps give the new PFE mode, which is independent of the position in depletion layer.