Suppression of short-channel effects in enhancement-mode GaN HEMTs utilizing graded-AlGaN barrier and lattice-matched quaternary InAlGaN back-barrier

This paper proposes and simulates a design for an enhancement-mode HEMT (GIB-HEMT) that combines a graded-AlGaN barrier layer with a lattice-matched InAlGaN back-barrier layer. The study systematically investigates the effects of the graded-barrier on band broadening and carrier distribution, as well as the mechanisms by which different In (and Al) contents and channel thicknesses modulate the device's electrical characteristics. Simulation results indicate that the graded-AlGaN barrier effectively reduces charge localization at the interface; the lattice-matched InAlGaN back-barrier significantly suppresses the leakage current by restricting carrier escape into the buffer. Key electrical parameters that were extracted from the optimized GIB-HEMT include a peak transconductance of 306.41 mS/mm and a saturation current of 755.46 mA/mm, operating at a threshold voltage of 1.28 V. Additionally, the architecture yielded impressive subthreshold and RF characteristics, specifically a drain-induced barrier lowering (DIBL) of 15 mV/V, a subthreshold swing (SS) of 99.2 mV/dec, coupled with a current-gain cutoff frequency of 71.8 GHz and a maximum oscillation frequency of 94.8 GHz. Furthermore, we investigated how increasing the length of T-shaped gate top degrades the frequency characteristics due to an increase in gate–source/drain capacitance. The device proposed in this paper combines stable normally-off operation, good DC output capability, and excellent RF performance, providing a viable device structure for suppressing short-channel effects and facilitating the RF characteristics of enhancement-mode GaN HEMTs.