Low-resistance ohmic contacts to N-face p-GaN for the fabrication of functional devices

The electrical properties of Ni-based ohmic contacts N-face p -type GaN are presented. The specific contact resistance of N-face p -GaN exhibits a liner decrease from 1.01 × cm 2 to 9.05 × 10 −3 Ω cm 2 for the as-deposited and the annealed Ni/Au contacts, respectively, with increasing annealing temperature Furthermore, the specific contact resistance could be decreased by four orders of magnitude to 1.03 × 10 −4 Ω cm 2 as a result of surface treatment using an alcohol-based (NH 4 ) 2 S solution. The depth profile data measured by the intensity of O1s core peak in the x-ray photoemission spectra showed that the alcohol-based (NH 4 ) 2 S treatment was effective in removing of the surface oxide layer of GaN. In addition, a Ga 2p core-level peak showed a red-shift of binding energy by 0.3 eV by alcohol-based (NH 4 ) 2 S treatment, indicating that the surface Fermi level was shifted toward the valence-band edge. Thus, the low ohmic contact behavior observed in our treated sample might be explained in terms of the removal of the oxide layer and reducing the barrier heights by reduced band-bending effect.