Investigation of flat band voltage shift in recessed-gate GaN MOSHFETs with post-metallization-annealing in oxygen atmosphere

Abstract

We have investigated the effects of post-metallization-annealing (PMA) in oxygen atmosphere on recessed-gate GaN metal-oxide-semiconductor heterostructure field effect transistors (MOSHFETs). The flat band voltage of MOS is a function of bulk and interface charges in the oxide, which strongly depends on a post-annealing process as well as deposition conditions. A positive threshold voltage shift enabling normally-off operation has been achieved by an O-2 PMA process where the GaN MOSHFET employed an ICPCVD SiO2 gate oxide with a Ni/Au metal gate. According to the analysis using energy dispersive x-ray spectroscopy in transmission electron microscopy and x-ray photoelectron spectroscopy, it is suggested that the improved SiO2/GaN interface quality with an enhanced metallic-like Ga level was responsible for the positive shift in threshold voltage.