ITO ∕ Ti ∕ Au Ohmic contacts on n-type ZnO

The specific contact resistivity and chemical intermixing of indium-tin-oxide (ITO)∕Ti∕Au Ohmic contacts on n-type bulk ZnO substrates are reported as a function of annealing temperature up to 450°C. A minimum contact resistivity of 4.6×10−6Ωcm2 was obtained at 50°C and the value remained <10−5Ωcm2 for all temperatures up to 450°C, suggesting that the Ti is an effective diffusion barrier which prevents formation of Au–In solid solutions. Optical microscopy of the contacts shows roughening of the morphology after annealing at 450°C. Indium outdiffusion to the surface of the contact stack is significant by 350°C, and Zn outdiffusion is evident by 450°C. Both the In and underlying Ti become oxidized after these higher temperature treatments.