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

• We systematically analyzed the V th , I on , and I off changes during stress-recovery in GaN MIS-HEMTs, comparing single-layer and bilayer gate insulators. • Dual-layer devices exhibited a smaller V th shift. • A significant decrease in I on was observed during the recovery stage, which we attributed to charge redistribution (lateral diffusion) from the insulator toward the gate-drain region. • By introducing an asymmetric recovery measurement method, we demonstrated that charge redistribution was effectively suppressed. • Reliability assessment requires considering not only V th but also current behavior, and the results can provide direct guidance for gate dielectric design and long-term reliability enhancement. 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 ( V th ) shift, on current ( I on ), and off current ( I off ). Bilayer devices with an additional aluminum oxide (Al 2 O 3 ) layer exhibit smaller V th shifts due to suppressed trapping. However, the analysis of the ion and I off changes of each device shows that during the recovery stage, I on ( I on, 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 V th for a more complete reliability assessment.