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Investigation of low- and high-resistance Ni–Ge–Au ohmic contacts to n+ GaAs using electron microbeam and surface analytical techniques

Published online by Cambridge University Press:  31 January 2011

Nancy E. Lumpkin ,
Gregory R. Lumpkin  and
K. S. A. Butcher
Nancy E. Lumpkin
Affiliation:
Division of Radiophysics, CSIRO, P.O. Box 77, Epping, New South Wales, 2121, Australia
Gregory R. Lumpkin
Affiliation:
Advanced Materials Program, Australian Nuclear Science and Technology Organisation, Private Mail Bag 1, Menai, New South Wales, Australia
K. S. A. Butcher
Affiliation:
Department of Physics, Semiconductor Science and Technology Laboratories, Macquarie University, New South Wales, 2109, Australia
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Abstract

A process for the formation of low-resistance Ni–Ge–Au ohmic contacts to n+ GaAs has been refined using multivariable screening and response surface experiments. Samples from the refined, low-resistance process (which measure 0.05 ± 0.02 Ω · mm) and the unrefined, higher resistance process (0.17 ± 0.02 Ω · mm) were characterized using analytical electron microscopy (AEM), transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and x-ray photoemission spectroscopy (XPS) depth profiling methods. This approach was used to identify microstructural differences and compare them with electrical resistance measurements. Analytical results of the unrefined ohmic process sample reveal a heterogeneous, multiphase microstructure with a rough alloy-GaAs interface. The sample from the refined ohmic process exhibits an alloy which is homogeneous, smooth, and has a fine-grained microstructure with two uniformly distributed phases. XPS analysis for the refined ohmic process sample indicates that the Ge content is relatively depleted in the alloy (relative to the deposited Ge amount) and enriched in the GaAs. This is not evidenced in the unrefined ohmic process sample. Our data lead us to conclude that a smooth, uniform, two-phase microstructure, coupled with a shift in Ge content from the post-alloy metal to the GaAs, is important in forming low-resistance ohmic contacts.

Type
Articles
Information
Journal of Materials Research , Volume 11 , Issue 5 , May 1996 , pp. 1244 - 1254
Copyright
Copyright © Materials Research Society 1996

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