We present a systematic approach to reduce the resistance of ohmic contacts on AlGaN/GaN FET structures. We have optimised the Ti/Al/Ni/Au contact with respect to the metal composition and annealing conditions. Our optimised contact has a very low contact resistance of 0.2 ohm mm (7.3 x 10^-7 ohm cm^2), a good reproducibility and an excellent line definition, making this contact very suitable for use in AlGaN/GaN FETs with short gate-source distances. This contact resistance on FET material is among the best values reported. The approach presented here can be applied to other metal schemes like Ti/Al/Pt/Au or Ti/Al/Ti/Au.
Jacobs, B., Krämer, M. C. J. C. M., Geluk, E. J., & Karouta, F. (2002). Optimisation of the Ti/Al/Ni/Au ohmic contact on AlGaN/GaN FET structures. Journal of Crystal Growth, 241(1/2), 15-18. https://doi.org/10.1016/S0022-0248(02)00920-X