Electro-structural evolution and Schottky barrier height in annealed Au/Ni contacts onto p-GaN

This paper reports on the evolution of the structural and electrical proprieties of Au/Ni contacts to p-type gallium nitride (GaN) upon thermal treatments. Annealing of the metals in an oxidizing atmosphere (N2/O2) led to better electrical characteristics, in terms of specific contact resistance (qc), with respect to non-reacting ambient (Ar). The evolution of the metal structures and the formation of a NiO layer both at the sample surface and at the interface with p-GaN were monitored by several techniques such as transmission electron microscopy (TEM), x-ray diffraction (XRD), and atomic force microscopy (AFM). Furthermore, a reduction of the Schottky barrier height from 1.07 eV (Ar annealing) to 0.71 eV (N2/O2 annealing) was determined by the temperature dependence of the qc. Local current maps by conductive AFM demonstrate the role of the interface in the conduction mechanism. These electrical results were correlated with the interfacial microstructure of the annealed contacts considering different transport models.