Performance enhancement of ohmic contact on n-GaN using Ti–W as metal barrier

Surface morphology and electrical performance of Ti/Al/metal/Au multilayer schemes were studied and compared to identify the role of the barrier layer on contact reliability. In this metallization scheme, Ti and Ti–W were tested as intermediate layer, and the optimal annealing parameters to form low-resistance ohmic contact were investigated. Besides, the effect of carrying out two-step annealing method in both metallizations was also evaluated. The result obtained was that the properties of ohmic contacts on n-GaN improved using Ti–W/Au as capping layer on Ti/Al bilayer, in comparison with using Ti/Au one. This enhancement became more evident when performing two-step annealing method. In this particular case, Ti–W-based contact not only delivered lower contact resistance, 0.25 ± 0.01 Ω mm versus 0.35 ± 0.01 Ω mm, but also better surface morphology and line edge definition. All these figures reveal the superior properties of Ti–W as metal barrier in comparison with standard contact based on Ti.