Effect of metal/semiconductor interface on the resistance of a nonalloyed p-GaN/Ni–Au contact

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The formation of an ohmic p-contact represents a critical step in the processing of GaN-based devices such as light-emitting diodes (LEDs). Thermal annealing in an O2-containing atmosphere at high temperature of a GaN/Ni–Au contact is mostly used today, while nonannealed contacts have been reported to provide much lower electrical performances. We experimentally evidence that the quality of the contact before annealing strongly depends on the nature of the Ni/GaN interface. Electrical results are correlated to microstructural and physicochemical analysis using high-resolution transmission scanning electron microscopy coupled with energy dispersive x-ray spectroscopy for this purpose. Using an annealed contact formed in standard conditions as a reference, we evidence from in situ treatment of the interface before metal evaporation that interfacial Ga-Oxide plays a detrimental role. We show that the metal evaporation conditions may strongly impact the physicochemical composition of the interface before annealing. We obtain nonannealed contact with electrical characteristics close to that of an annealed, standard one, using a reduced evaporation rate, in our evaporation conditions. This result is of interest for the processing of p-GaN contacts at a low thermal budget.