High-Frequency Performance of GaN High-Electron Mobility Transistors on 3C-SiC/Si Substrates With Au-Free Ohmic Contacts

As an alternative to the standard Au-based ohmic contacts, in this letter, Ti/TiN contacts were used to fabricate GaN high-electron mobility transistors (HEMTs) with two barrier designs (Al_0.2Ga_0.8N/AlN and Al_0.35Ga_0.65N). The ohmic contact resistance for this Au-free metallization scheme with a very smooth surface morphology is 0.13 Qmm and the specific contact resistance is ~10^-6 Ωcm². Our best 100-nm gate transistors show a maximum drain current density of 1.13 A/mm and a peak extrinsic transconductance of 388 mS/mm. The fastest transistors with a gate length of 80-nm achieve cutoff frequencies of 176 GHz, rivaling the fastest GaN HEMTs on silicon and silicon carbide substrate with comparable gate length and Au-based ohmic contacts.