Study of the electrical and structural characteristics of Al/Pt ohmic contacts on n-type ZnO epitaxial layer

We have investigated Al/Pt (20/50 nm) ohmic contacts on a n-type zinc oxide (ZnO:Al) epitaxial layer. The samples were annealed at temperatures of 300degreesC and 600degreesC for 1 min in nitrogen ambient. Current-voltage measurements indicated that the as-deposited sample was ohmic with a specific contact resistivity of 1.25 (+/-0.05) x 10(-5) Omega cm(2). However, the annealing at 300degreesC resulted in a significantly better ohmic behavior, with a contact resistivity of 2 (+/-0.25) x 10(-6) Omega cm(2). A further increase in the annealing temperature to 600degreesC led to a decrease in specific contact resistivity due to extensive interfacial reactions between Al and ZnO. Both Auger electron spectroscopy and glancing angle X-ray diffraction were employed to investigate the nature of the interfacial reaction between the Al/Pt and ZnO layer with increasing annealing temperature. Possible explanation is given to describe the temperature dependence of the specific contact resistivity. (C) 2004 The Electrochemical Society.