Microstructural and electrical investigation of Pd/Au ohmic contact on p-GaN

Interfacial microstructure, elemental diffusion, and electrical properties of Pd/Au ohmic contact to p-type GaN have been investigated using scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy. The as-deposited sample exhibits the formation of an ohmic contact which is fundamentally due to epitaxial relationship between the Pd, Au and GaN layer. Pd nanocrystals are formed with crystallographic orientation with respect to the substrate described as follows (111)_Pd//(0001)_GaN, [11¯0]_Pd// [112¯0]_GaN. Thermal annealing at 800 °C leads to the formation of majority phase composed by crystalline Au rich Au₆-Pd₂-Ga composites, with crystallographic orientation of (11¯0)Au6-Pd2-Ga//(0001)_GaN, and minority phases, which are composed of Au₅-Pd₂-Ga₂, Au₃-Pd₂-Ga₃, and Ga₂-Pd₅, which is responsible for the formation of an ohmic contact with a specific contact resistance of 1.04 × 10^-2 Ω cm².