H. Yazdani, S. Chevtchenko, F. Brunner, G. Tränkle, and J. Würfl
phys. stat. sol (a), vol. 219, no. 8, pp. 2100802, doi: 10.1002/pssa.202100802 (2022).
Herein, the fabrication of Au-free ohmic contacts for mm-wave GaN heterojunction field-effect transistors is investigated. To find an optimum metal stack and annealing recipe, different metallization and rapid thermal annealing temperature/duration combinations are tested. They are compared with the well-known Ti/Al/Ni/Au ohmic contact scheme optimized for AlGaN/GaN epitaxial structures. Herein, a Ta/Al/Ta metal stack is initially fabricated and analyzed. Subsequently, further developments for improving the contact resistance and surface roughness of Ta-based ohmic contacts are carried out. The best achieved Au-free contact resistance is ≈0.28±0.18Ωmm for Ta/Al/W metallization after annealing at 600°C. The root mean square (RMS) surface roughness and edge definition in this contact are improved significantly to 7.5 nm RMS and about 30 nm edge accuracy compared with 16 nm RMS and 160 nm in Au-based contacts.
Ferdinand-Braun-Institut gGmbH, Leibniz-Institut für Höchstfrequenztechnik (FBH), Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany
Au-free ohmic contacts, GaN HEMTs, 2D electrons gases
© 2022 The Authors. physica status solidi (a) applications and materials science published by Wiley-VCH GmbH.
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Full version in pdf-format.