Investigation of Electrical Property and Thermal Stability in Enhancement-Mode InxAl1–xN/AlN/GaN MOS-HEMTs Fabricated by Using NiOx Gate and Fluorine Treatment

In this study, we report a novel approach for achieving high-performance enhancement mode (E-mode) InAlN/GaN MOS HEMTs based on the fluorine treatment and a p-type NiOx gate (F-NiO HEMT). The NiO film was deposited at different substrate temperatures using reactive sputtering in a varied mixture of O2 and Ar. We show that the threshold voltage $({V}_{TH}$ ) is effectively modulated by comprehensively optimizing fluorine ion implantation and NiO sputtering conditions without requiring gate recess etching. The influence of different NiO deposition conditions on electrical properties and the critical interface of NiOx/InAlN have been investigated in detail. The proposed E-mode F-NiO HEMT exhibits superior on-state characteristics, including more positive ${V}_{TH}$ , enhanced gate voltage swing, larger transconductance ${g}_{m}$ and also superior gate control over the channel. The dual C-V and pulsed mode measurements confirm the excellent NiOx/AlInN interface and effective suppression of current collapse. We propose a model to explain the contrasting temperature-dependent coefficients of ${V}_{TH}$ shifts observed in pure fluorine ion-implanted and NiO-based devices. The underlying mechanisms at elevated temperatures are also analyzed.