Enhancement Mode N-Polar Deep Recess GaN HEMT With Record Small Signal Performance

In this letter, we report a novel enhancement mode N-polar Deep Recess (NPDR) Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT). Enhancement mode operation was achieved by recess etching with a combination of atomic layer etching (ALE) and wet etching. A high-k and high breakdown field HfSiO gate dielectric was employed. The epi-structure was grown on a low dislocation density on-axis N-polar GaN substrate by plasma-assisted molecular beam epitaxy (PAMBE). As a result, true normally-off operation with +0.8V threshold voltage, 1.5 A/mm peak saturation drain current, and 0.55 S/mm transconductance was achieved with 75 nm gate length (LG). A cutoff frequency (fT) of 122 GHz was measured, which resulted in a record fT*LG of 9.1 GHz $\cdot \mu $ m for E-mode AlGaN/GaN HEMTs. Load pull measurements demonstrated an output power of 2.7 W/mm and a power-added efficiency of 46% at 10 GHz.