T-gate with dual dielectric layer for p-GaN/AlGaN/GaN HFETs: Suppressed gate leakage current and increased gate voltage range

In this paper, a T-shaped gate with a dual dielectric layer is proposed for enhancement-mode p-GaN/AlGaN/GaN heterojunction field-effect transistors (HFETs), designed to reduce gate leakage current and improve gate forward breakdown voltage. The proposed dual dielectric layer, comprising Al₂O₃ and SiO₂ films, modulates the energy band structure at the gate edge to suppress the hole injection from the gate metal to the p-GaN layer. As a result, the p-GaN/AlGaN/GaN HFET with the proposed T-shaped gate demonstrated a significantly reduced gate leakage current of ∼ 10^-7 A/mm at V_GS = 8 V and a substantially higher gate forward breakdown voltage of 16 V, compared to a conventional structure with a gate leakage current of ∼ 10^-3 A/mm at V_GS = 8 V and a gate forward breakdown voltage of 8.5 V. Additionally, the off-state breakdown voltage of the proposed device was noticeably improved. These results suggest that the proposed dual dielectric configuration offers a promising approach to overcoming the limited gate voltage range of conventional p-GaN/AlGaN/GaN HFETs, thereby enhancing device reliability.