Barrier heights and Fermi level pinning in metal contacts on p-type GaN

In this work, we investigate the current–voltage (I–V) characteristics of various metal contacts such as Ni/Au, Ir/Au, Ru/Au, Mo/Au, and W/Au on p-GaN. For this, we fabricated different bilayer metal contacts on the same epitaxial heterostructure of GaN, which ensures the uniformity of the experimental data. I–V measurements were then carried out for circular and/or linear contact pads with different spacing values. In each case, the Schottky barrier height of the metal contacts is calculated using the reverse I–V method. A strong Fermi level pinning was found in all these structures on p-GaN, with a pinning factor of ∼0.15. In addition, a very low Ohmic contact resistivity of 3.45 × 10−6 Ω cm2 was measured for the Ru/Au contacts on p-GaN.