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Cross-Section Transmission Electron Microscope Study of Ni/Au/Ge/Au Ohmic Contact to Gallium Arsenide

Published online by Cambridge University Press:  26 February 2011

Taeil Kim
Affiliation:
Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon University, Pittsburgh, PA 15213
D. D. L. Chung
Affiliation:
Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon University, Pittsburgh, PA 15213
S. Mahajan
Affiliation:
Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon University, Pittsburgh, PA 15213
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Abstract

The interfacial structures resulting from the metallurgical reactions between a Ni/Au/Ge/Au film and (100) GaAs substrate were studied by cross-section TEM. Annealing at 300 – 350°C causes a complicated solid-solid phase reaction, resulting in the multilayer structure of Ni2Ge/Au7Ga2/NiAs/Au7Ga,/GaAs. The contact shows non-ohmic character, since most of the doping element Ge is trapped in the surface Ni2Ge layer When the contact is annealed at above 400°C. the layered structure is destroyed because one of the phases (Au-Ga) becomes liquid but other phases (Ni-Ge, Ni-As) remain solid Ge, which is captured in the surface layer, diffuses out of the Ni2Ge phase into the contact/GaAs interface through the Au-rich melt. Above this temperature, a Ge-doped n+ region is probably formed at the NiAs/GaAs interface and the contact becomes ohmic. With increasing annealing temperature, continuous grain growth of NiAs is found to occur and the NiAs/GaAs interface area increases. Thus the ohmic behavior of Au-Ge-Ni on n-GaAs can be explained by the low barrier height of the NiAs/GaAs interface and the formation of Ge-doped n+ region under the NiAs phase.

Type
Articles
Copyright
Copyright © Materials Research Society 1987

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References

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