Schottky barrier heights of Au, Pd and Ni on n-GaN evaluated using mesa-structure diodes

We investigated the Schottky characteristics of Au, Pd and Ni on n-GaN using capacitance-voltage and current-voltage measurements for mesa-structure diodes. Even though these metals have a similar metal work function of around 5.1 eV, their Schottky barrier heights are considerably different each other. The obtained Schottky barrier heights are 0.96, 1.50 and 1.34 eV for Au, Pd and Ni, respectively. The high Schottky barrier height for Pd is preferable for the gate metal in a field effect transistor and the ohmic metal for p-type nitride semiconductor. Although the work function difference between Au and Pd is just 0.02 eV, the barrier height difference is as high as 0.54 eV, meaning that the interfacial reaction between these metals and GaN or the Fermi-level pinning mechanism is quite different.