SiNx Prepassivation of AlGaN/GaN High-Electron-Mobility Transistors Using Remote-Mode Plasma-Enhanced Chemical Vapor Deposition

The surface of AlGaN/GaN high-electron-mobility transistors (HEMTs) tends to be easily damaged during device fabrication, especially during high-temperature annealing. In order to resolve this problem, a prepassivation process was developed using remote-mode plasma-enhanced chemical vapor deposition (RPECVD) systems. It is important in the prepassivation process to protect the region under the gate during high-temperature ohmic annealing and utilize a low-damage SiN x etching process to minimize any surface damage. It was observed that the DC characteristics were significantly improved and the current collapse phenomenon was markedly suppressed for AlGaN/GaN HEMTs by employing the prepassivation process proposed in this work in comparison with a conventional process. According to the experimental results, the prepassivation process coupled with a gate field plate successfully suppressed the current collapse phenomenon in AlGaN/GaN HEMTs. RF output power densities of 6.9 W/mm at 2.3 GHz and >8.9 W/mm at 4 GHz were achieved for AlGaN/GaN HEMTs on Si and SiC substrates, respectively.