Microstructure, electrical properties, and thermal stability of Al ohmic contacts to n-GaN

L. L. Smith, R. F. Davis, M. J. Kim, Ray Carpenter, Y. Huang

Research output: Contribution to journalArticlepeer-review

34 Scopus citations


As-deposited Al contacts were ohmic with a room-temperature contact resistivity of 8.6 × 10-5 Ω · cm2 on Ge-doped, highly n-type GaN (n = 5 × 1019 cm-3). They remained thermally stable to at least 500 °C, under flowing N2 at atmospheric pressure. The specific contact resistivities (ρc) calculated from TLM measurements on as-deposited Al layers were found to range from 8.6 × 10-5 Ω · cm2 at room temperature and 6.2 × 10-5 Ω · cm2 at 500 °C. Annealing treatments at 550 °C and 650 °C for 60 s each under flowing N2 resulted in an overall increase of contact resistivity. Cross-sectional, high-resolution electron microscopy (HREM) revealed that interfacial secondary phase formation occurred during high-temperature treatments, and coincided with the degradation of contact performance. Electron diffraction patterns from the particles revealed a cubic structure with lattice constant a = 0.784 nm, and faceting occurring on the {100} faces. Spectroscopic analysis via electron energy loss spectroscopy (EELS) revealed the presence of nitrogen and small amounts of oxygen in the Al layer, but no appreciable amounts of Ga. The results of microstructural and crystallographic characterization indicate that the new interfacial phase is a type of spinel Al nitride or Al oxynitride.

Original languageEnglish (US)
Pages (from-to)2257-2262
Number of pages6
JournalJournal of Materials Research
Issue number9
StatePublished - Sep 1996

ASJC Scopus subject areas

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


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