Importance of Scaling in RF GaN HEMTs for Reduction of Surface Traps‐Induced Drain Lag

Abstract

Drain lag is a well‐known phenomenon that leads to radio frequency performance degradation in AlGaN/GaN high‐electron‐mobility transistors. Herein, it is demonstrated that a reduction of the gate‐to‐drain distance (Lgd) from 2.0 to 0.5 μm results in 7% reduction in the current collapse. This improvement is attributed to a decrease in surface trapping, which, in this case, is found to have a greater impact on current collapse than relatively slow traps in the buffer layer. To support this argument, TCAD simulations are conducted. Load‐pull analysis confirms that scaling the devices to Lgd = 0.5 μm provides 15% better output power density at 10 GHz than Lgd = 2.0 μm. Additionally, a new passivation layer for reduced surface traps exhibits a 20 to 30% higher output power density and at least a 10% improvement in power‐added efficiency at 20 GHz on a nominally identical GaN‐on‐semi‐insulating SiC epi‐wafer.