Improvement of Subthreshold Characteristic of Gate-Recessed AlGaN/GaN Transistors by Using Dual-Gate Structure

Abstract

The subthreshold characteristic of gate-recessed high-electron-mobility transistors (HEMTs) using dual-gate (DG) architectures is systematically studied. The recessed DG structure can effectively shift the threshold voltage ( ${V}_{\text {th}}$ ) in the positive direction. Different from the complex function expression between ${V}_{\text {th}}$ and AlGaN thickness ( $\text{t}_{b}$ ) in the recessed single-gate (SG) device, the variation of $\text{V}_{\text {th}}$ with ${t}_{b}$ is monotonic in the recessed DG devices. Recessed DG device exhibits a low off-state leakage current of $\sim {3}\times {10}^{{-10}}$ A/mm and gate induced drain leakage is effectively improved. A higher $I_{ \mathrm{\scriptscriptstyle ON}}/I_{ \mathrm{\scriptscriptstyle OFF}}$ range of recessed DG devices broadens about 2 times and provide a wider range of ${t}_{b}$ than that of recessed SG devices. The DG structure has a stronger modulation effect on drain–source resistance ( ${R}_{\text {ds}}$ ) and gate–drain resistance ( ${R}_{\text {gd}}$ ) than the SG devices. A lower subthreshold swing (SS) of ~100 mV/dec is obtained by recessed DG design. Due to the second gate inducing the lateral extension of depletion region between the first gate and drain, the off-state leakage and first gate reverse leakage have been significantly improved. Therefore, the recessed DG architecture design can effectively improve the fluctuation of SS and off-state current versus the different AlGaN barrier thickness.