Crystal structure of low-resistance Au-Ni/p-GaN contacts

The atomic arrangement of Ni-Au contacts on p-type GaN has been studied by transmission electron microscopy. A sharp transition between GaN and Au is observed, with no intermediate phases present. Lattice parameter measurements of the Au layer reveal that the Au layer is fully relaxed. The epitaxial relationship between the Au layer and the GaN film is (111)Au//(0002)GaN, [110]Au//[1120]GaN. Careful analysis of lattice images indicates that Au is directly in contact with Ga on p-GaN. Ni, which is used primarily as a wetting later, is not present at the interface. The separation between Ga and Au atoms at the interface was found to be 2.5Å. Comparison of experimental and calculated images gives a best match for the interface separation obtained by TEM that corresponds to covalent Ga bonded to metallic Au, with a bond length of 2.5 Å.