High-performance Ka-band AlN-buffer GaN HEMTs with enhanced dynamic and breakdown characteristics achieving 10.05 W/mm <i>P</i> sat and 53.05% PAE

Abstract

This work presents a high-performance Ka-band GaN high electron mobility transistor (HEMT) utilizing an undoped AlN buffer layer to replace the conventional Fe-doped GaN buffer. This AlN-buffer structure eliminates deep-level traps associated with Fe doping, leading to improved dynamic performance. Drain current transient measurements under semi-on state stress show a current collapse of 8.5% for the AlN-buffer HEMT (AlN-B HEMT), lower than the 15.7% observed in the Fe-doped GaN buffer HEMT (GaN-B HEMT). Furthermore, the wide bandgap and high critical field of AlN effectively enhance channel confinement and breakdown voltage. Compared to the conventional GaN-B HEMT, the AlN-B HEMT demonstrates a notably higher off-state breakdown voltage (124 vs 67 V) and lower off-state leakage. Large-signal characterization at 30 GHz demonstrates that the scaled AlN-B HEMT achieves a saturated output power density of 10.05 W/mm and a peak power-added efficiency of 53.05% at a drain bias of 25 V. This performance is competitive with state-of-the-art N-polar GaN HEMTs, confirming the undoped AlN-buffer structure as a highly promising pathway for developing high-performance power amplifiers in the Ka-band.