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

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 (Vth) in the positive direction. Different from the complex function expression between Vth and AlGaN thickness (tb) in the recessed single-gate (SG) device, the variation of Vth with tb is monotonic in the recessed DG devices. Recessed DG device exhibits a low off-state leakage current of ~ 3 × 10^-10 A/mm and gate induced drain leakage is effectively improved. A higher ION/IOFF range of recessed DG devices broadens about 2 times and provide a wider range of tb than that of recessed SG devices. The DG structure has a stronger modulation effect on drain-source-resistance (Rds) and gate-drain resistance (Rgd) 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.