N-Polar GaN Deep Recess HEMT With Atomic Layer Deposition HfO $_{\text{2}}$ as Gate Insulator

N-polar GaN deep recess high electron mobil-ity transistors (HEMTs) with metal-organic chemical vapor deposition (MOCVD) SiN(x)SiNx gate dielectric have been shown to achieve record output powers and efficiencies in W-band. This study investigates the use of thermal atomic layer deposition (ALD) HfO2 as the gate dielectric in deep recess N-polar GaN HEMTs for the first time. DC measure-ments showed a peak transconductance of 420 mS/mm, a gate leakage current of 140 nA/mm, and a dielectric break-down field of 6.2 MV/cm. Importantly, near-zero hysteresis was observed in dc measurements and pulsed I-V mea-surements showed less than 5% dispersion. A unity current gain frequency (f(T)) of 30.5 GHz and a maximum oscillation frequency (f(MAX)) of 53 GHz were measured. These results show the potential of using HfO2 as a gate dielectric in the future ultra scaled N-polar deep recess GaN HEMTs.