Quality of the Oxidation Interface of AlGaN in Enhancement-Mode AlGaN/GaN High-Electron Mobility Transistors

摘要

Enhancement-mode AlGaN/GaN high-electron mobility transistors (HEMTs) were realized by applying the $hbox{O}_{2}$ and $ hbox{N}_{2}hbox{O}$ plasma oxidation method to the AlGaN Schottky layers. After the postannealing process, the threshold voltage $V_{rm th}$ of conventional depletion-mode GaN HEMTs was $-$3.1 V, and this value was shifted to $+$0.3 V when either $ hbox{N}_{2}hbox{O}$ or $hbox{O}_{2}$ plasma oxidation treatment was used. X-ray photoelectron spectroscopy (XPS) analysis revealed that both treatments formed an $hbox{Al}_{2}hbox{O}_{3}/hbox{Ga}_{2}hbox{O}_{3}$ compound oxide layer. The decomposition of N–O bonds in the $hbox{N}_{2}hbox{O}$ plasma suppressed the formation of nitrogen vacancy traps and ensured low roughness of the AlGaN surface during oxidation. This nitridation process also reduced the $hbox{1}/f$ noise.