Observation of Quasi-Saturation Phenomenon in Sidewall Gate GaN Vertical Transistors

We report the observation of quasi-saturation behavior in GaN vertical metal oxide semiconductor field-effect transistors featuring a sidewall-gate architecture. Compared to conventional trench-gate designs, the sidewall-gate structure exhibits pronounced drain current roll-off and negative transconductance under high gate bias. This degradation is consistent with space charge modulation, wherein localized electron accumulation at the gate-drift interface distorts the electric field distribution and limits carrier mobility. Comprehensive electrical characterization and technology computer-aided design simulations reveal how asymmetric gate geometry affects vertical and lateral electron spreading paths. These findings highlight the role for mitigating field-induced current degradation in vertical GaN power devices.