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

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Abstract
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 ( ${R}_{\text {C}}\text {)}$ of $0.18~\Omega~\cdot $ 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 ( ${g}_{\text {m}}\text {)}$ of 302.2mS/mm and a saturation drain current ( ${I}_{\text {D, {max}}}\text {)}$ of 1.26 A/mm. Small-signal radio frequency (RF) measurements yield a cutoff frequency ( ${f}_{\text {T}}\text {)}$ of 23.9 GHz and a maximum oscillation frequency ( ${f}_{\max }\text {)}$ of 38.9 GHz. Furthermore, the TSD HEMT demonstrates an output power density ( ${P}_{\text {sat}}\text {)}$ 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.
Funding Information
  • National Natural Science Foundation of China (62404165)
  • National Natural Science Foundation of China (62474135)
  • National Natural Science Foundation of China (62234009)
  • National Natural Science Foundation of China (62574152)
  • National Natural Science Foundation of China (QTZX26127)
  • Postdoctoral Fellowship Program of CPSF (GZB20230557)
  • China Postdoctoral Science Foundation (2023M732730)
  • Natural Science Basic Research Program of Shaanxi (2024JC-YBQN-0611)

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