Ti/Al/Ni/Au and Ti/Al/Pt/Au multi-layer ohmic contacts on Al/sub x/Ga/sub 1-x/N/GaN heterostructures

The ohmic contacts of Ti/Al/Ni/Au and Ti/Al/Pt/Au multi-layer on unintentionally-doped Al/sub 0.22/Ga/sub 0.78/N/GaN heterostructures have been investigated. The specific contact resistivities of 1.26/spl times/10/sup -6/ /spl Omega//spl middot/cm/sup 2/ for Ti/Al/Ni/Au contact and 1.97 /spl times/ 10/sup -5/ /spl Omega//spl middot/cm/sup 2/ for Ti/Al/Pt/Au contact were obtained. It is found that the Pt element in Ti/Al/Pt/Au multi-layer influent the diffusion of Al atom into the Au layer, which results in the higher contact resistivity of Ti/Al/Pt/Au contact than that of Ti/Al/Ni/Au one. The formation of excellent ohmic contact on the Al/sub 0.22/Ga/sub 0.78/N/GaN heterostructures is attributed to the existing of a compatible barrier between the metal electrode and the carrier channel at the Al/sub 0.22/Ga/sub 0.78/N/GaN hetero-interface. The width of the barrier depends on the annealing temperature and duration.