Low-resistance and highly transparent Ag/IZO ohmic contact to p-type GaN

The electrical, structural, and optical characteristics of Ag/ZnO-doped In2O3 (IZO) ohmic contacts to p-type GaN:Mg (2.5 x 1017 cm-3) were investigated. The Ag and IZO (10 nm/50 nm) layers were prepared by thermal evaporation and linear facing target sputtering, respectively. Although the as-deposited and 400 oC annealed samples showed rectifying behavior, the 500 and 600 oC annealed samples showed linear I-V characteristics indicative of the formation of an ohmic contact. The annealing of the contact at 600 oC for 3 min in a vacuum (∼ 10-3 Torr) resulted in the lowest specific contact resistivity of 1.8 x 10-4 Ω.cm2 and high transparency of 78% at a wavelength of 470 nm. Using Auger electron spectroscopy, depth profiling and synchrotron X-ray scattering analysis, we suggested a possible mechanism to explain the annealing dependence of the electrical properties of the Ag/IZO contacts.