Low-Leakage and High-Breakdown Enhancement-Mode InAlGaN/GaN HEMTs Using a Non-Recessed Mist-CVD Li-Doped NiO/Al 2 O 3 p-Gate Stack

Enhancement-mode (E-mode) InAlGaN/GaN high-electron-mobility transistors (HEMTs) are highly desirable for fail-safe power and RF applications; however, achieving stable normally-off operation without inducing plasma damage remains challenging due to the strong polarization effects in InAlGaN barriers. In this work, non-recessed E-mode InAlGaN/GaN HEMTs enabled by a mist chemical vapor deposition (mist-CVD)–grown Li-doped NiO/Al2O3p-gate stack are demonstrated. The Al2O3interlayer serves as a low-damage interface buffer and leakage-suppression dielectric, while the p-type Li-doped NiO layer provides active electrostatic modulation to effectively deplete the polarization-induced two-dimensional electron gas without gate recessing. Compared with undoped p-NiO and Al2O3-only gate configurations, the Li-doped NiO (p-Li:NiO) device exhibits clear enhancement-mode operation with the threshold voltage shifting from −2.36 V to +0.32 V. A high maximum transconductance of 498 mS/mm and an increased saturation drain current of 523 mA/mm are achieved, together with a substantially suppressed gate leakage current of 9.8 × 10-9mA/mm atVG= −10 V. Moreover, the p-Li:NiO-gated HEMT demonstrates an exceptional off-state breakdown voltage of 2423 V (ID= 1 nA/mm), resulting in a Baliga’s figure of merit of 2.14 GW/cm2. Long-term DC bias stress measurements up to 15,000 s reveal minimal drain-current degradation and excellent threshold-voltage stability, confirming the robustness of the proposed gate stack. These results establish mist-CVD Li-doped NiO/ Al2O3p-gate engineering as a reliable and process-compatible solution for high-performance, non-recessed enhancement-mode InAlGaN/GaN HEMTs targeting next-generation GaN power electronic applications.