The electrical properties of single Pt (30 nm) and Pt (30nm)/Ni (30nm)/Au (50nm) multilayer contacts on moderately doped p-ZnO(N-a = 5.0 x 10(17)/cm(3)) were investigated. Although linear current -voltage characteristics were observed for all samples, a sample that was annealed for 1 min at a temperature above 500 degrees C resulted in an ohmic contact with good characteristics. The best ohmic contact to p-type ZnO was obtained using a Pt/Ni/Au multilayer contact that was annealed at 600 degrees C for 1 min under a N-2 ambient, showing a specific contact resistance R-c of 1.97 x 10(-5) Omega cm(2). The fundamental mechanisms for the lower contact resistivity of Pt/Ni/Au contacts are discussed based on glancing-angle X-ray diffraction results and Auger depth profile analysis of the multilayer alloying process. Furthermore, we fabricated a ZnO p-n homojunction using Pt/Ni/Au and Ti/Au as the p-type and n-type ohmic contact metal, respectively. The threshold voltage was determined to be about 3.7 V, comparable to the bandgap energy of ZnO. (c) 2006 The Electrochemical Society.