253 GHz f_T Graded‐Channel AlGaN/GaN High‐Electron‐Mobility Transistors with New Cliff Barrier for Millimeter Wave High‐Frequency Applications

In this research work, a graded‐channel AlGaN/GaN high‐electron‐mobility transistor (HEMT) featuring a cliff AlGaN barrier with a gate length of 60 nm is investigated. The inclusion of a foot cliff barrier layer confines the 3DEG distribution, thereby reducing electron scattering and potentially improving carrier mobility. The cliff‐graded‐channel device shows a peak cutoff frequency f_T of 253 GHz and power‐added efficiency of 68% at 30 GHz, which represents a significant 60% improvement in comparison with conventional graded‐channel devices. These results clearly indicate that the graded‐channel AlGaN/GaN HEMT with a new cliff barrier design has great potential for mmW applications.