High Breakdown Voltage in RF AlN/GaN/AlN Quantum Well HEMTs

Abstract

In evaluating GaN high-electron mobility transistors (HEMTs) for high-power applications, it is crucial to consider the device-level breakdown characteristics. This letter replaces the conventional AlGaN barrier and common AlGaN backbarrier with unstrained AlN, and it assesses the breakdown voltage of AlN/GaN/AlN quantum well HEMTs for gate-drain spacings in the range of 0.27– $5.1~\mu \text{m}$ . The results are highlighted by a high breakdown voltage of 78 V for a gate-drain spacing of 390 nm, among the best reported for submicron-channel devices. In addition, small-signal RF measurements showed record performance for HEMTs on the AlN platform, with $\text {f}_{\text {t}}/\text {f}_{\text {max}} = {161}/{70}$ GHz. The cut-off frequency and corresponding drain bias are benchmarked against the state-of-the-art GaN HEMTs using the Johnson figure of merit, with measured devices highlighted by a JFoM value of 2.2 THz $\cdot $ V. These results illustrate the potential for AlN/GaN/AlN quantum well HEMTs as a future platform for high-power RF transistors.