N-polar GaN-based MIS-HEMTs for mixed signal applications

GaN-based transistors are attractive for the next-generation RF power and mixed signal electronics due to their high breakdown field and high carrier saturation velocity. III-N high electron mobility transistors (HEMTs) fabricated on the N-face of GaN are well-suited to address the problems of poor electron confinement and high ohmic contact resistance in the highly scaled transistors. At 4 GHz, N-polar metal-insulator-semiconductor (MIS)-HEMTs with a gate length of 0.7 μm exhibited a highest output power density (P_out) of 8.1 W/mm and a highest power-added efficiency (PAE) of 71%, while a P_out of 4.2 W/mm and a PAE of 49% were achieved at 10 GHz. A high speed N-polar MIS-HEMT fabricated with a gate-first self-aligned InGaN-based ohmic contact regrowth technology was characterized, demonstrating an ultra-low contact resistance of 23 Ω-μm and a state-of-the-art f_T·L_G product of 16.8 GHz-μm with a gate length of 130 nm.