Rapid thermal annealing induced changes on the contact of Ni/Au to N-doped ZnO

Abstract: N-doped p-type ZnO (p∼1018cm-3) was grown on sapphire(0001) substrate by metal-organic chemical vapor deposition method. Ni/Au metal was evaporated on the ZnO film to form contacts. As-deposited contacts were rectifying while ohmic behavior was achieved after thermally annealing the contacts in nitrogen environment. Specific contact resistance was determined by circular transmission line method and a minimum specific contact resistance of 8×10−4 Ωcm2 was obtained for the sample annealed at 650°C for 30s. However, Hall effect measurements indicate that, as the rapid thermal annealing temperature increased up to 550°C or higher the samples’ conductive type have changed from p-type to n-type, which may be due to the instability nature of the present-day p-type N-doped ZnO or the dissociation of ZnO caused by annealing process in N2 ambient. Evolution of the sample''s electric characteristics and the increment of metal/semiconductor interface states induced by rapid thermal annealing process are supposed to be responsible for the improvement of electrical properties of Au/Ni/ZnO. [Copyright &y& Elsevier]