Reduction of ohmic contact resistivity on p-GaN using N2 plasma surface treatment at room temperature

Abstract

A reduction of Ni/Au ohmic contact resistivity on p-type GaN was obtained by surface treatment using N2 plasma at room temperature. For p-type GaN with a hole concentration of about 1 × 1017 cm−3, the contact resistivity decreased from 5.0 × 10−2 Ω cm2 to 3.1 × 10−4 Ω cm2 by the N2 plasma treatment, compared to that of the HCl only-treated sample. The O 1s core-level peak in the x-ray photoemission spectra shows that the N2 plasma treatment is effective in the removal of the surface oxide layer. Compared to the HCl only-treated surface, the surface Fermi level on the N2 plasma-treated surface lies about 0.58 eV closer to the valence band edge, resulting in a much smaller surface barrier height to p-GaN than the HCl only-treated surface. The smaller surface barrier height of p-GaN treated with N2 plasma can lead to a lower contact resistivity and can play an important role in lowering the metal contact resistivity to p-GaN.