S-parameter and perfect pinning of the Fermi level at nonpolar (11-20) a-plane p-GaN surfaces

We investigated the Schottky barrier height and S-parameter at nonpolar (11-20) a-plane p-GaN surfaces by using Schottky diodes fabricated with various metals, including Ti, Cu, Ni, and Pt. A barrier inhomogeneity model was used to explain anomalous carrier transport behavior at the nonpolar p-GaN surfaces, yielding the mean barrier heights of 2.01, 1.73, 1.82, and 1.92eV for the Ti, Cu, Ni, and Pt contacts, respectively. The extracted S-parameter was as low as 0.02, indicating perfect pinning of the surface Fermi level at around 1.9eV above the valence band.