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

In 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 ( ${V}_{\text {th}}{)}$ shift and ON-state current ( ${I}_{\text {on}}{)}$ variation are observed. However, after a recovery period, the degradation trend of ${V}_{\text {th}}$ and that of ${I}_{\text {on}}$ are in opposite directions. Such opposite degradations 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 generation. 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.