This study investigated the gate capacitance and off-state characteristics of 650-V enhancement-mode p-GaN gate AlGaN/GaN high-electron-mobility transistors after various degrees of gate stress bias. A significant change was observed in the on-state capacitance when the gate stress bias was greater than 6 V. The corresponding threshold voltage exhibited a positive shift at low gate stress and a negative shift when the gate stress was greater than 6 V, which agreed with the shift observation from the I–V measurement. Moreover, the off-state leakage current increased significantly after the gate stress exceeded 6 V during the off-state characterization although the devices could be biased up to 1000 V without breakdown. The increase in the off-state leakage current would lead to higher power loss.

AlGaN/GaN high-electron-mobility transistors with different channel configurations were fabricated and characterized. Channel configuration was designed to have the source, gate, and drain metal contacts of the same size but with different channel widths, which was achieved by the current blocking region. Current density, subthreshold swing, and transconductance (gm) improved with the decreasing channel width. A significant improvement was observed in gm because of a large gate width (WG) to channel width (Wchannel) ratio. A device with a WG/Wchannel of 4 has a gm of 239 mS/mm, whereas a device with a WG/Wchannel of 1 has a gm of 127 mS/mm.