Impact of process-dependent SiNx passivation on proton-induced degradation in GaN MIS-HEMTs

In this study, AlGaN/GaN heterojunction-based metal–insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) were fabricated using silicon nitride (SiN) passivation layer. This layer was deposited under the different gas ratio conditions. The effects of proton irradiation on the current characteristics of the devices were investigated according to the deposition conditions of the SiN film. The drain current (ID) characteristics of two devices (with Si-rich or N-rich SiN passivation layers) were reduced by proton irradiation regardless of the deposition condition of SiN film because of the proton-induced displacement damage. In terms of the threshold voltage (Vth), off-state current (Ioff) and gate leakage current (IG), the device with Si-rich SiN exhibited less variation after proton irradiation compared with the N-rich SiN device. This is because the Si-rich SiN was less affected by the proton irradiation. Furthermore, the device with Si-rich SiN showed better dynamic performances before and after proton irradiation than the device with N-rich SiN. This was achieved suppressing the drain-lag phenomenon because the high SiH4 rate for Si-rich SiN deposition considerably reduces the bulk trap states. The capacitance characteristics of the Si-rich SiN device were also improved by the high SiH4 rate. Therefore, the Si-rich SiN-passivated MIS-HEMTs achieved enhanced performance and higher reliability for applications involving space radiation.