Comparison between TiAl and TiAlNiAu ohmic contacts to n-type GaN

We report a comparison between Ti/Al and Ti/Al/Ni/Au ohmic contacts in term s of contact resistivity, thermal stability, depth profile, and surface mor phology. The metals were deposited by conventional electron-beam evaporatio n, and then annealed at 900 degrees C for 30 s in a N-2 atmosphere. The low est value for the specific contact resistivity was obtained using Ti/Al/Ni/ Au metallization. Ti/Al/Ni/Au contacts showed no increase in contact resist ivity after aging for five days at 600 degrees C in an air atmosphere. Exam ination of the surface morphology using atomic force microscopy revealed th at the surface roughness was clearly better in the case of Ti/Al/Ni/Au cont acts. X-ray photoelectron spectroscopy was also employed and gave primary r esults of Ti/Al/Ni/Au contact formation.