Investigation of Threshold Voltage and Drain Current Degradations in Si3N4/AlGaN/GaN MIS-HEMTs Under X-Ray Irradiation

this study, X-ray irradiation of metal- insulator-semiconductor (MIS) AlGaN/GaN high-electron-mobility transistors (HEMTs) is performed. After the X-ray irradiation, the threshold voltage (V-th) shift and ON-state current (I-on) variation are observed. However, after a recovery period, the degradation trend of V-th and that of I-on are in opposite directions. Such opposite degra-dations are demonstrated and explained in this study. As X-rays irradiate the devices, holes, and defects are generated in the GaN layer and Si3N4 layer, respectively. To prove the degradation mechanism induced by X-rays in MIS HEMT, the following characteristics are offered. The drain current (I-d) and the source current (I-s) under the X-ray irradiation are introduced to prove the hole gener-ation. The two-step degradation of the gate current (I-g) after X-ray irradiation provides evidence of the formation of defect states. Moreover, the different degradation behaviors between Schottky-gate HEMT and MIS HEMT are compared and verification of the position of generation of defect states in the Si3N4 layer is given accordingly.