Fabrication and Characteristics of AlInN/AlN/GaN MOS-HEMTs with Ultra-Thin Atomic Layer Deposited Al₂O₃ Gate Dielectric

Al_0.85In_0.15N/AlN/GaN metal−oxide-semiconductor high electron mobility transistors (MOS-HEMTs) employing a 3-nm ultra-thin atomic-layer deposited (ALD) Al₂O₃ gate dielectric layer are reported. Devices with 0.6 μm gate lengths exhibit an improved maximum drain current density of 1227 mA/mm at a gate bias of 3 V, a peak transconductance of 328 mS/mm, a cutoff frequency f_T of 16 GHz, a maximum frequency of oscillation f_max of 45 GHz, as well as significant gate leakage suppression in both reverse and forward directions, compared with the conventional Al_0.85In_0.15N/AlN/GaN HEMT. Negligible C–V hysteresis, together with a smaller pinch−off voltage shift, is observed, demonstrating few bulk traps in the dielectric and high quality of the Al₂O₃/AlInN interface. It is most notable that not only the transconductance profile of the MOS-HEMT is almost the same as that of the conventional HEMT with a negative shift, but also the peak transconductance of the MOS-HEMT is increased slightly. It is an exciting improvement in the transconductance performance.