Effect of rapid thermal annealing on a Ti/Au ohmic contact to n-ZnO

We deposited Ti (20 nm)/Au (60 nm) layers on n-ZnO in order to produce low-resistivity ohmic contacts by using a dc sputtering method. The samples were annealed at various temperatures for 1 min in an air ambient. The electrical and the structural properties of the Ti/Au contact to n-ZnO were investigated. The current-voltage measurement showed that the as-deposited and annealed samples exhibited an ohmic behavior. The specific contact resistance of the sample annealed at 300°C was 5.6 × 10^-4 Ω·cm². Further increasing the temperature caused the ohmic behavior to be degraded. The X-ray diffraction (XRD) pattern was used to characterize the crystal quality of the Ti/Au contact layers. The XRD results showed that the crystallinity of the Au layer was improved when it was annealed at 300°C for 1 min. Further annealing caused the crystallinity to be degraded. We concluded that the improvement in the annealed Ti/Au contacts to n-ZnO might be due to an increased ohmic contact area caused by postgrowth thermal annealing.