The reduction in the gate leakage current and the improvement in subthreshold characteristics and current collapse in AlGaN/GaN highelectron-mobility transistors (HEMTs) with various surface treatments were investigated. We applied wet treatment, digital etching (O 2 or N 2 O), or plasma treatment (CF 4 or SF 6) before SiN x passivation. Among these treatments, SF 6 plasma treatment suppressed gate leakage current, reduced subthreshold slope, and improved pulsed current-voltage (I-V) characteristics most effectively.

An investigation of threshold voltage instability in gate recessed normally-off GaN metal insulator semiconductor high electron mobility transistors (MIS-HEMTs) was performed by analyzing the interface states, border traps, and conduction band offset. To reduce the threshold voltage instability with improved dielectric-GaN interface, plasma enhanced atomic layer deposition (PEALD) technique was successfully employed for very thin SiNx (5nm) as an interfacial layer. Forward biased gate leakage current, capacitance-voltage measurements, andcurrent-transient analysis were performed to find the reason for this improvement. Finally, we proposed an importance of border traps and the conduction band offset which is related to trapping mechanism in transfer characteristics.