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 300°C and 600°C 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) × 10^-5 Ω cm². However, the annealing at 300°C resulted in a significantly better ohmic behavior, with a contact resistivity of 2 (±0.25) × 10^-6 Ω cm². A further increase in the annealing temperature to 600°C led to a decrease in specific contact resistivity due to extensive interfacial reactions between AI 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.