Comparison of AlGaN/GaN insulated gate heterostructure field-effect transistors with ultrathin Al2O3/Si3N4 bilayer and Si3N4 single layer

Device performances have been compared between two types of AlGaN/GaN metal-insulator-semiconductor heterostructure field effect transistors (MIS-HFETs) with Al2O3/Si3N4 bilayers and a Si3N4 single layer. Al2O3/Si3N4 bilayer-based MIS-HFETs have much lower gate current leakage than Si3N4-based MIS devices by more than 3 orders of magnitude under reverse gate biases. An ultralow gate leakage of 1 x 10(-11) A/mm at -15 V has been achieved in the Al2O3/Si3N4 bilayer-based MIS devices though higher maximum drain-source current has been obtained in the Si3N4-based MIS devices. A maximum transconductance of more than 180 mS/mm with ultra-low gate leakage has been achieved in the ultrathin Al2O3/Si3N4 bilayer-based MIS-HFET device with a gate length of 1.5 mu m, which is much higher than that of less than 130 mS/mm in the Si3N4-based MIS devices. The reduction in the transconductance of Al2O3/Si3N4 bilayer-based devices was much smaller than that in the Si3N4-based MIS devices due to the employment of ultrathin bilayers with a large dielectric constant. This work demonstrates that an Al2O3/Si3N4 bilayer insulator is a superior candidate for nitride-based MIS-HFET devices.