Dislocation induced nonuniform surface morphology of Ti/Al/Ni/Au Ohmic contacts to AlGaN/GaN HEMTs

In this study, Ti/Al/Ni/Au Ohmic contact to AlGaN/GaN high electron mobility transistors was fabricated and demonstrated distribution of bright and dark areas on the surface. Surface element analyses show that it is of great difference in the Ni and Au content between these two kinds of regions. According to transmission electron microscopy and corresponding Electron dispersive x-ray spectroscopy analyses, plenty of Ni was detected in dislocation rich regions while rare Ni was left in dislocation free regions so that Au tended to accumulate in the form of AlAu_x binary alloy. The surface nonuniformity presented on the surface should be attributed to the nonuniform interfacial reactions resulted from the dislocations.