Simulation Study of Enhancement-Mode HEMTs with Graded AlGaN Barriers and GaN/InGaN Double Quantum Well Caps

This study proposes an enhancement-mode high electron mobility transistor (HEMT) with a six-region graded Al0.25Ga0.75N barrier layer, divided into three lateral and two vertical segments with varying Al compositions. To mitigate increased gate leakage from reduced Al content under the gate, an InGaN layer is inserted into the p-GaN cap to form a GaN/InGaN double quantum well (DQW), suppressing leakage. However, the reverse piezoelectric polarization at the GaN/InGaN interface reduces saturation current, which is compensated by N-well buried layers in the channel. Compared to conventional AlGaN/GaN HEMTs, the optimized device achieves a 13.7% higher saturation current (Isat = 1657.5 mA/mm), 27% higher threshold voltage (Vth = 4.2 V), and 22.1% lower gate leakage (1.92 × 10−4 A/mm).