Ag-ZnO co-sputtered films at various atomic ratios of Ag (Ag/(Ag + Zn) at.%) were prepared by a radio frequency magnetron cosputtering system, using the co-sputtered targets of Ag and ZnO. The activation of the Ag acceptors (AgZn) and the formation of the Ag aggregations (Ag0) in the ZnO matrix were investigated from XRD, Raman scattering, and XPS measurements. The Ag-ZnO co-sputtered film behaving like a p-type conduction was achievable after annealing at 350 °C under air ambient for 1 h.

Transparent indium tin oxide (ITO) and cosputtered ITO-zinc oxide (ZnO) films' contacts to an n-GaN epilayer were investigated. Both of these electrodes' contact to the n-GaN epilayer showed Schottky behavior, although the contact resistance of the ITO-ZnO/n-GaN system was lower than that of the ITO/n-GaN system. By placing a thin Ti interlayer between the ITO-ZnO/n-GaN interface, nonalloyed ohmic contact was achieved. The inset Ti interlayer was both beneficial both for enhancing the outdiffusion of the nitrogen atoms at the surface of the n-GaN and suppressing the indiffusion of oxygen atoms from the surface of the ITO-ZnO to n-GaN. The figure-of-merit (FOM), evaluated from the specific contact resistance and optical property of the Ti/ITO-ZnO system's contact to the n-GaN epilayer, was optimized further at an adequate thickness of the Ti interlayer.