Metal/nonpolar m-plane ZnO contacts with and without thin Al₂O₃ interlayer deposited by atomic layer deposition

Using the temperature dependent current–voltage (I–V) measurements, the electrical properties of Au/nonpolar m-plane ZnO Schottky diodes with an Al₂O₃ interlayer prepared by atomic layer deposition (ALD) was investigated. With an Al₂O₃ interlayer, it was found to have higher barrier heights and higher rectifying ratio. Modified Richardson plots produced effective Richardson constants of 30.0 and 37.6 Acm⁻²K⁻² for the samples with and without Al₂O₃ interlayer, respectively, which are similar to the theoretical value of 32.0 Acm^{− 2}K^{− 2} for n-ZnO. Scanning transmission electron microscope (STEM) results showed that the oxygen-contained layer on ZnO surface degraded the film quality of subsequently deposited Al₂O₃ layer. In addition, the inter-diffusion of Au and Al atoms into ZnO subsurface region also modulated the electrical properties of Au/ZnO contacts.