N-Polar GaN Deep Recess HEMT With Atomic Layer Deposition HfO2 as Gate Insulator

N-polar GaN deep recess high electron mobility transistors (HEMTs) with metal-organic chemical vapor deposition (MOCVD) SiNxSiN ${x}$ 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 measurements showed a peak transconductance of 420 mS/mm, a gate leakage current of 140 nA/mm, and a dielectric breakdown field of 6.2 MV/cm. Importantly, near-zero hysteresis was observed in dc measurements and pulsed ${I}$ – ${V}$ measurements showed less than 5% dispersion. A unity current gain frequency ( ${f}_{T}{)}$ of 30.5 GHz and a maximum oscillation frequency ( ${f}_{\text {MAX}}{)}$ 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.