Novel GaN-based MOS HFETs with thermally oxidized gate insulator

GaN-based MOS HFETs with gate oxides formed by direct thermal oxidation of AlGaN/GaN epi layers have been developed for the first time. The fabricated MOS HFETs have exhibited high breakdown voltages, low gate leakage currents and stable operation at high drain voltages. Although MOS HFET with an undoped channel showed a reduced maximum drain current of 400 mA/mm, higher drain currents up to 900 mA/mm has been obtained by adopting a doped-channel structure. The stable device operations at high drain voltages indicate that the trap density at the interface between the thermal oxide and epi layers will be low and the thermal oxide can be also used as a passivation film.