Microstructure of Ti/Al and Ti/Al/Ni/Au Ohmic contacts for <i>n</i>-GaN

DOI PDF 15 Citations
  • S. Ruvimov
    Materials Sciences Division, Lawrence Berkeley National Laboratory, University of California, MS 62-203, Berkeley, California 94720
  • Z. Liliental-Weber
    Materials Sciences Division, Lawrence Berkeley National Laboratory, University of California, MS 62-203, Berkeley, California 94720
  • J. Washburn
    Materials Sciences Division, Lawrence Berkeley National Laboratory, University of California, MS 62-203, Berkeley, California 94720
  • K. J. Duxstad
    Department of Materials Science and Mineral Engineering, University of California at Berkeley, Berkeley, California 94720
  • E. E. Haller
    Department of Materials Science and Mineral Engineering, University of California at Berkeley, Berkeley, California 94720
  • Z.-F. Fan
    Materials Research Laboratory and Coordinated Science Laboratory, University of Illinois, Urbana-Champaign, Illinois 61810
  • S. N. Mohammad
    Materials Research Laboratory and Coordinated Science Laboratory, University of Illinois, Urbana-Champaign, Illinois 61810
  • W. Kim
    Materials Research Laboratory and Coordinated Science Laboratory, University of Illinois, Urbana-Champaign, Illinois 61810
  • A. E. Botchkarev
    Materials Research Laboratory and Coordinated Science Laboratory, University of Illinois, Urbana-Champaign, Illinois 61810
  • H. Morkoç
    Materials Research Laboratory and Coordinated Science Laboratory, University of Illinois, Urbana-Champaign, Illinois 61810

Abstract

<jats:p>Transmission electron microscopy has been applied to characterize the structure of Ti/Al and Ti/Al/Ni/Au Ohmic contacts on n-type GaN (∼1017 cm−3) epitaxial layers. The metals were deposited either by conventional electron-beam or thermal evaporation techniques, and then thermally annealed at 900 °C for 30 s in a N2 atmosphere. Before metal deposition, the GaN surface was treated by reactive ion etching. A thin polycrystalline cubic TiN layer epitaxially matched to the (0001) GaN surface was detected at the interface with the GaN substrate. This layer was studied in detail by electron diffraction and high resolution electron microscopy. The orientation relationship between the cubic TiN and the GaN was found to be: {111}TiN//{00.1}GaN, [110]TiN//[11.0]GaN, [112]TiN//[10.0]GaN. The formation of this cubic TiN layer results in an excess of N vacancies in the GaN close to the interface which is considered to be the reason for the low resistance of the contact.</jats:p>

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