Normally-off AlGaN/GaN MOS-HEMT using ultra-thin Al0.45Ga0.55N barrier layer

In this work, we report on the fabrication of a normally-off AlGaN/GaN Metal–Oxide–Semiconductor High Electron Mobility Transistor (MOS-HEMT) using an ultra-thin Al0.45Ga0.55N barrier layer. The AlGaN barrier was thinned down to 1 nm using a digital etching process (Oxidation/Etching) and was followed by a PECVD deposition technique of a 7 nm thick SiOx layer used as gate insulator. Thanks to the thin AlGaN barrier layer (4 nm), only a few digital etching cycles are required to shift the threshold voltage toward positive values. The fabricated normally-off device exhibits a pinch-off voltage of +1.1 V, a maximum IDS current of 460 mA mm−1 at VGS = +5 V, an On-state resistance (RON) of 7.8 Ω · mm and an ION/IOFF ratio higher than 109. Moreover, the pulsed IDS–VDS and capacitance–voltage (C–V) curves versus frequency confirm that there is no damage induced by the digital etching process.