Optimisation of the Ti/Al/Ni/Au ohmic contact on AlGaN/GaN FET structures

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