Charge lateral diffusion in MIS-HEMTs and its influence on stress and recovery conditions with single and bilayer insulators

This study investigates the impact of charge trapping and diffusion on the electrical characteristics of gallium nitride (GaN) metal–insulator-semiconductor high electron mobility transistors (MIS-HEMTs) with single layer and bilayer of gate insulator during stress and recovery conditions. Transfer curve measurements are conducted to analyze the threshold voltage (Vth) shift, on current (Ion), and off current (Ioff). Bilayer devices with an additional aluminum oxide (Al2O3) layer exhibit smaller Vth shifts due to suppressed trapping. However, the analysis of the ion and Ioff changes of each device shows that during the recovery stage, Ion (Ion, recovery) decreases due to charge redistribution from the gate insulator to the gate-drain region. An asymmetric recovery measurement method is introduced, applying a negative voltage to both the gate and drain terminals, effectively suppressing charge redistribution. These results provide critical insights into the trapping and diffusion mechanisms in GaN MIS-HEMTs and highlight the importance of analyzing current behavior alongside Vth for a more complete reliability assessment.