Quaternary Enhancement-Mode HFET With In Situ SiN Passivation

A lattice-matched InAlGaN/GaN heterostructure with a barrier-layer thickness of 4 nm has been grown and passivated in situ with a 63-nm SiN by metal-organic chemical vapor deposition. Enhancement-mode heterostructure field-effect transistors have been realized by a fluorine-based surface treatment after the local removal of the SiN. The threshold voltage and transconductance were 0.65 V and 250 mS/mm, respectively, for a 1-μm gate-length device. The benefits of an in situ SiN passivation are demonstrated: first, the stabilization of the barrier material and prevention from oxidation and second, the improvement of the device characteristics by reduced source resistance and reduced trapping effects.