High performance normally-off recessed-gate GaN-based MIS-HEMTs achieved by oxygen plasma treatment

We report on the high performance normally-off recessed-gate GaN-based MIS-HEMTs exhibiting excellent combination of maximum drain current (>600 mA/mm) and high positive threshold voltage (+1.3 V) achieved by oxygen plasma treatment. Using the positive threshold voltage shift phenomena previously demonstrated in oxygen plasma treated planar MIS-HEMTs, we were able to achieve robust enhancement-mode operation employing a relatively thick 9-nm-AlGaN barrier layer in the channel region. The rather thick AlGaN barrier may have suppressed remote scattering from insulator/AlGaN interface states leading, to high maximum drain current.

I. Introduction

Thanks to intrinsic properties derived from the wide bandgap of gallium nitride (GaN), GaN-based high-electron-mobility transistors (HEMTs) are fulfilling its promise of unprecedented performance in high-frequency and high-power applications [1 , 2] . Our group has demonstrated improved performance in terms of reduced current collapse in AlGaN/GaN Schottky-gate HEMTs subjected to oxygen plasma treatment [3 , 4] . However, these devices are normally-on due to the default presence of two dimensional electron gas (2DEG) along the channel. Normally-off devices with positive threshold voltage ( V _TH ) are preferred for simpler gate drive topology and fail-safe operation. Recently, we have reported positive V _TH shift phenomena in planar Al ₂ O ₃ /AlGaN/GaN MIS-HEMTs whose AlGaN surface was subjected to oxygen plasma treated prior to Al ₂ O ₃ dielectric deposition [5] . In this study, we report on the electrical performance of recessed-gate Al ₂ O ₃ /AlGaN/GaN MIS-HEMTs and demonstrate its promise in solving the longstanding problem of the tradeoff between maximum drain current ( I _D,max ) and V _TH in GaN-based MIS-HEMTs [6] .