AVS 54th International Symposium | |
Electronic Materials and Processing | Thursday Sessions |
Session EM-ThP |
Session: | Electronic Materials and Processing Poster Session |
Presenter: | L.F. Voss, University of Florida |
Authors: | L.F. Voss, University of Florida L. Stafford, University of Florida R. Khanna, University of Florida B.P. Gila, University of Florida C.R. Abernathy, University of Florida F. Ren, University of Florida I.I. Kravchenko, University of Florida |
Correspondent: | Click to Email |
We examined the potential of transition metal nitrides as a diffusion barrier for Ti/Al-based Ohmic contacts to n-GaN and Ni/Au-based Ohmic contacts to p-GaN. The annealing temperature (600-1000°C) dependence of Ohmic contact characteristics using either Ti/Al/X/Ti/Au (n-Ohmics) or Ni/Au/X/Ti/Au (p-Ohmics) metallization schemes, where X is TaN, TiN, or ZrN, deposited by plasma-assisted sputtering were investigated by contact resistance and Auger Electron Spectroscopy (AES) measurements. For n-GaN (n~3x1017 cm-3), the as-deposited contacts were rectifying and transitioned to Ohmic behavior for annealing at ≥600°C. A minimum specific contact resistivity of ~6x10-5Ω.cm-2 was obtained after annealing over a broad range of temperatures (600-900°C for 60 secs), comparable to that achieved using a conventional Ti/Al/Pt/Au scheme on the same wafer. The contact morphology became considerably rougher at the high end of the annealing range. The long-term reliability of the contacts was also examined-each contact structure showed an increase in contact resistance by a factor of 3-4 over 24 days at 350°C in air. AES profiling showed that long-term aging had little effect on the nitride-based contact structure. For annealing temperatures greater than 500°C, the contacts to p-GaN (p~1017 cm-3) displayed Ohmic characteristics and reached a minimum specific contacts resistance of about 2x10-4Ω.cm2 after annealing at 700°C for 60 s. The specific contact resistance was stable on annealing up to at least 1000°C. However, at high temperatures the morphology of the contacts became very rough and a large degree of intermixing between the metallic layers was observed. The thermal stability of these contacts were found to be superior as compared to conventional Ni/Au, which displayed poor characteristics at anneal temperatures greater than 500°C.