Transient extension process of the off-state depletion region in GaN HEMTs with SiO2 passivation

This Letter investigates the transient extension process of the off-state depletion region along the channel in SiO2-passivated GaN HEMTs based on a channel-probe branch structure. An SiO2 passivation layer was deposited to partially suppress the surface traps and decelerate the dynamic extension process of the depletion region, facilitating measurements of the extension time of the depletion region (τext) at various probe distances (Ldp) under identical off-state conditions. For Ldp < 4 μm, the depletion region extended quickly, then it slowed down and extended with a saturated extension rate for Ldp > 4 μm. Technology Computer Aided Design simulation was performed to help understand the transient extension process of the depletion region. An exponential dependence of τext on the drain–gate bias (VDG) was also observed, which is due to the Poole–Frenkel emission-dominated surface trapping process under off-state conditions. The steady-state potential profile along the channel is also discussed.