Fabrication and Performance of Ti/Al/Ni/TiN Au-Free Ohmic Contacts for Undoped AlGaN/GaN HEMT

作者：Li, Xianhui; Gao, Sheng; Zhou, Quanbin; Liu, Xiaoyi; Hu, Wenlong; Wang, Hong^*

来源：IEEE Transactions on Electron Devices, 2020, 67(5): 1959-1964.

DOI：10.1109/TED.2020.2982665

• AlGaN/GaN high-electron-mobility transistor (HEMT)
• Au-free ohmic contacts
• contact resistance
• root-mean-square (rms) roughness
• TiN film

We proposed a preparation method of a TiN capping layer compatible with the ohmic contacts process, and demonstrated the Au-free ohmic contacts of an undoped AlGaN/GaN high-electron-mobility transistor (HEMT) with a Ti/Al/Ni/TiN metal structure. TiN was prepared through depositing Ti thin film by a sputtering system and then annealing in N-2 ambient by the rapid thermal annealingprocess. The thickness of Ti/Al, annealing temperature, and annealing time were investigated systematically. Using the Ti/Al/Ni/TiN structure, a low contact resistance (3.47 x 10(-5) Omega cm(2), 1.1 Omega.mm) was obtained when annealed at 900 degrees C for 30 s in N-2 ambient, which was comparable with conventional Au-based ohmic contacts (3.12 x 10(-5) Omega.cm(2), 1.05 Omega.mm). In addition, the Ti/Al/Ni/TiN ohmic contacts showed smooth surface morphology with a surface roughness of 5.89 nm. AlGaN/GaN HEMT, based on Ti/Al/Ni/TiN Au-free ohmic contacts, was also fabricated and exhibited good dc characteristics. The reported Au-free AlGaN/GaN HEMT fabrication process can be used in standard Si fabs without the risk of contamination.