High-PAE Gold-Free AlGaN/GaN HEMT With Al–Si Alloy Gate Fabrication Process for 5G Applications

In this article, we present gold-free AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on SiC substrates using an Al–Si alloy gate fabrication process. The proposed devices incorporate a two-step deposited (TSD) Ti/Al/Ti/TiN metal stack with high-dose ion-implanted ohmic regions and implement an ohmic trench etching technique. This design achieves an ultralow ohmic contact resistance (RC)of0.18~Ω~·mm and a highly uniform surface morphology with a root-mean-squared (rms) roughness of 2.33 nm. In addition, the gate electrode employs a Ti/AlSi metal stack that is fully compatible with Si-based CMOS technology. Owing to the superior ohmic contact properties, the fabricated HEMTs exhibit a peak transconductance (gₘ)of 302.2mS/mm and a saturation drain current (I_ D, max)of 1.26 A/mm. Small-signal radio frequency (RF) measurements yield a cutoff frequency (fT)of 23.9 GHz and a maximum oscillation frequency (fₘₐₓ)of 38.9 GHz. Furthermore, the TSD HEMT demonstrates an output power density (Pₛₐₜ)of 3.9 W/mm and a peak power-added efficiency (PAE) of 63.1% at 3.6GHz. These findings highlight the potential of this approach in advancing high-performance and low-cost Au-free GaN HEMTs for sub-6 GHz RF applications.