The influence of contact composition, pretreatment, and annealing gas on the ohmic behavior of Ti/Al-based ohmic contacts to n-A10.4Ga 0.6N

K. O. Schweitz, T. G. Pribicko, S. E. Mohney, T. F. Isaacs-Smith, J. Williams, M. Pophristic, D. Gotthold, R. Birkhahn, I. Ferguson

Research output: Chapter in Book/Report/Conference proceedingConference contribution

2 Scopus citations


As the group III nitride semiconductor technology matures, an increasing number of devices are being fabricated with high Al fraction AlGaN. In this study, ohmic behavior is achieved using Ti/Al/Pt/Au contacts to n-Al 0.4Ga0.6N, which is the highest Al fraction for which ohmic contact formation has been reported. The effect of contact composition, pretreatment, and annealing conditions is studied by 30 s isochronal annealing experiments between 500°C and 1000°C. A specific contact resistance ρc of (5±3)×10-5 Ωcm2 is obtained using Ti(26 nm)/Al(74 nm)/Pt(50 nm)/Au(50 nm) contacts to n-Al 0.4Ga0.6N annealed in N2 at 800°C; however, this value is shown to be artificially high because the metal sheet resistance RM is 4 Ω/, causing an artifact in the data analysis. All contacts with ρc < 10-3 Ωcm2 exhibit a local minimum in ρc after annealing at 800°C. The observed increase in pc upon annealing at 850°C and 900°C, however, is not an artifact originating from a change in RM. The top Au layer is found to play an active role in forming ohmic contacts with low ρc, since omitting the Au layer yields an increase in ρc of two orders of magnitude after annealing at 800°C. Furthermore, leaving out the Au layer requires an annealing temperature of 700°C to result in linear I-V curves for currents up to 100 μ A, as opposed to 500°C when the Au layer is present. The role of Au is further studied in Ti(26 nm)/Al(74 nm)/Ni(50 nm)/Au(50 nm) contacts, where Rutherford backscattering spectroscopy reveals Ga in the metal layer and/or Au buried deeper than the original semiconductor-metal interface, and x-ray diffraction indicates the formation of new phases to happen concurrently with a decrease in ρc of three orders of magnitude.

Original languageEnglish (US)
Title of host publicationWide-Bandgap Electronics
Number of pages6
StatePublished - 2001
Event2001 MRS Spring Meeting - San Francisco, CA, United States
Duration: Apr 16 2001Apr 20 2001

Publication series

NameMaterials Research Society Symposium Proceedings
ISSN (Print)0272-9172


Other2001 MRS Spring Meeting
Country/TerritoryUnited States
CitySan Francisco, CA

All Science Journal Classification (ASJC) codes

  • General Materials Science
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering


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