PECVD SiNx passivation for AlGaN/GaN HFETs with ultra-thin AlGaN barrier

We have investigated the effects of a silicon nitride (SiNx) passivation process using plasma-enhanced chemical vapor deposition (PECVD) on a ultra-thin-barrier AlGaN/GaN heterostructure field-effect transistors (HFETs). The bulk charge characteristics of the PECVD SiNx films were dependent on the film deposition conditions, which strongly influenced the sheet resistance (Rsh) and flat-band voltage characteristics of AlGaN/GaN HFETs. The reduction in Rsh is a strong function of the amount of positive bulk charges in the SiNx passivation film. An optimized PECVD SiNx process was used to drastically decrease the Rsh from 45,450 Ω/sq to 732 Ω/sq. A Mo/Au Schottky-gate device fabricated with PECVD SiNx passivation exhibited a maximum drain current density of 172 mA/mm, quasi-normally-off operation, and breakdown voltage of > 1100 V