Comparison of AlGaN/GaN insulated gate heterostructure field-effect transistors with ultrathin Al₂O₃/Si₃N ₄ 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. Al₂O ₃/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 × 10^-11 A/mm at -15V has been achieved in the Al ₂O₃/Si₃N₄ bilayer-based MIS devices though higher maximum drain-source current has been obtained in the Si ₃N₄-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 μm, 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/Si ₃N₄ 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.