Ir/Au ohmic contacts on bulk, single-crystal n-type ZnO

The contact characteristics on bulk single-crystal n-type ZnO of an IrAu metallization scheme deposited by sputtering are reported as a function of annealing temperature in the range 200-1000°C (N2 ambient). The contacts exhibited ohmic behavior for all temperatures and show a minimum specific contact resistivity of 3.6× 10-5 cm2 after a 1000°C anneal. The contacts transition to rectifying behavior after annealing above 1100°C, coincident with a degraded surface morphology including agglomeration of Ir to the surface and heavy intermixing of the Ir and Au. The Ir contacts exhibit higher thermal stability but poorer specific contact resistivity than conventional TiAu metal stacks on bulk n-type ZnO. The contacts showed very little change in resistance after extended aging (30 days) at 350°C. Annealing under O2 ambient led to an increase in contact resistivity by orders of magnitude.