Dependence of the Au/Ni/Si/Ni contact properties on the Si-layer thickness and the annealing temperature in p-type GaN epilayers

The dependences of the properties of Au/Ni/Si/Ni contacts, deposited on p-GaN epilayers by using electron-beam evaporation, on the Si layer thickness and the annealing temperature were investigated with the goal of producing contacts with low specific resistances. The results of the current-voltage (I-V) curves showed that the lowest specific contact resistance obtained for the Au/Ni/Si/Ni contact with a 1200-Angstrom-thick Si layer on p-type GaN annealed at 700 degreesC for 1 min in a nitrogen atmosphere was 8.49 x 10(-4) Omega cm(2). The x-ray diffraction (XRD) measurements on the annealed Au/Ni/Si/Ni/p-GaN/sapphire heterostructure showed that Ni3Si, GaAu, and NiGa layers were formed at the Au/Ni/Si/Ni/p-GaN interfaces. While the intensities corresponding to the Ni3Si layer decreased with increasing annealing temperature above 700 degreesC, those related to the GaAu and the NiGa layers increased with increasing temperature. These results indicate that the Au/Ni/Si/Ni contacts with 1200-Angstrom-thick Si layers annealed at 700 degreesC hold promise for potential applications in p-GaN-based optoelectronic devices.