AlGaN/GaN-based metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs) with Al 2 O 3 /Si 3 N 4 bilayer as insulator have been investigated in detail, and compared with the conventional HFET and Si 3 N 4 -based MIS-HFET devices. Al 2 O 3 /Si 3 N 4 bilayer-based MIS-HFETs exhibited much lower gate current leakage than conventional HFET and Si 3 N 4 -based MIS devices under reverse gate bias, and leakage as low as 1 ϫ 10 Ϫ11 A/mm at Ϫ15 V has been achieved in Al 2 O 3 /Si 3 N 4 -based MIS devices. By using ultrathin Al 2 O 3 /Si 3 N 4 bilayer, very high maximum transconductance of more than 180 mS/mm with ultra-low gate leakage has been obtained in the MIS-HFET device with gate length of 1.5 µm, a reduction less than 5% in maximum transconductance compared with the conventional HFET device. This value was much smaller than the more than 30% reduction in the Si 3 N 4 -based MIS device, due to the employment of ultra-thin bilayer with large dielectric constant and the large conduction band offset between Al 2 O 3 and nitrides. This work demonstrates that Al 2 O 3 /Si 3 N 4 bilayer insulator is a superior candidate for nitrides-based MIS-HFET devices.

PACS 72.80. Ey, 73.40.Qv, 85.30.Tv The device performance of AlGaN/GaN-based metal-insulator-semiconductor heterostructure field effect transistors (MIS-HFETs) with a very thin AlGaN barrier and a heavily doped GaN channel for high 2DEG density has been investigated at elevated temperatures up to 250• C. The devices exhibited ultra-low gate current leakages under the reverse gate bias with very reasonable transconductance characteristics at both RT and high temperatures. MIS-HFETs with doped channel showed much higher saturation drain current and weaker current collapse than the conventional devices at RT and high temperatures.