AlGaN/GaN-based metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs) with Al2O3/Si3N 4 bilayer as insulator have been investigated in detail, and compared with the conventional HFET and Si3N4-based MIS-HFET devices. Al2O3/Si3N4 bilayer-based MIS-HFETs exhibited much lower gate current leakage than conventional HFET and Si3N4-based MIS devices under reverse gate bias, and leakage as low as 1 × 10-11 A/mm at -15 V has been achieved in Al2O3/Si3N4-based MIS devices. By using ultrathin Al2O3/Si3N4 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 Si3N4-based MIS device, due to the employment of ultra-thin bilayer with large dielectric constant and the, large conduction band offset between Al2O3 and nitrides. This work demonstrates that Al2O3/Si3N4 bilayer insulator is a superior candidate for nitrides-based MIS-HFET devices.
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