Effects of Thermal Annealing on the Au/Ni and the Au/Ni/Si/Ni Contact Properties of p-type GaN Epilayers

Thermal annealing effects on Au/Ni and Au/Ni/Si/Ni layers deposited on p-GaN epilayers by electron beam evaporation were employed with the goal of producing ohmic contacts with low specific resistance. Current–voltage (I–V) measurements were carried out to investigate the effects of thermal annealing on Au/Ni and Au/Ni/Si/Ni contact properties of p-type GaN epilayers, and X-ray photoelectron spectroscopy (XPS) measurements were performed to characterize the formation of the alloy layer and the diffusion behavior at each interface due to thermal treatment. The results of the I–V curves showed that both as-deposited and annealed Au/Ni and Au/Ni/Si/Ni contacts on p-GaN were high quality and that the lowest specific contact resistance of 5.32×10-2 Ω·cm2 was obtained for Au/Ni/Si/Ni annealed at 800°C for 1 min in a nitrogen atmosphere. The results of the X-ray diffraction and XPS measurements showed that Ni silicide layers were formed at the Au/Ni/Si/Ni/p-GaN interfaces. These results indicate that the formation of the Ni silicide layer due to thermal annealing reduces the specific contact resistance of the Au/Ni/Si/Ni contacts and that the Au/Ni/Si/Ni contacts annealed at 800°C hold promise for potential applications in optoelectronic devices.