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Stable Pt/Ge/Au Ohmic Contact to N-GaAs with a Ta-Si-N Barrier

Published online by Cambridge University Press:  22 February 2011

J. S. Chen ,
E. Kolawa ,
R. P. Ruiz  and
M-A. Nicolet
J. S. Chen
Affiliation:
California Institute of Technology, Pasadena, CA 91125
E. Kolawa
Affiliation:
California Institute of Technology, Pasadena, CA 91125
R. P. Ruiz
Affiliation:
Jet Propulsion Laboratory, Pasadena, CA 91109
M-A. Nicolet
Affiliation:
California Institute of Technology, Pasadena, CA 91125
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Abstract

A Pt/Ge/Au contact of the structure: <n-GaAs>/Pt(17nm)/Ge(25nm)/Au(43nm), overlaid with a Ta-Si-N barrier layer and a Au metallization layer has a contact resistivity, ρc, of 3.7×10−6 Ωcm2 after annealing at 450°C for 15 min. After aging at 450°C for 60 h, ρc slightly degrades to 5.5×10−6 Ωcm2 while the surface keeps smooth. When alloyed at 550°C for 15 min, ρc is 1.8×10−6 Ωcm2 and stays about the same value after annealing at 550°C for 1 h. Without the Ta-Si-N barrier and the Au overlayer, the Pt/Ge/Au contact alone is also ohmic after annealing at 450°C for 15 min but with a ρc of ∼10−5 Ωcm2 while the surface morphology deteriorates significantly after aging at 450°C for 20 h.

The thermal reactions of this Pt/Ge/Au contact on GaAs, with or without a Ta-Si-N barrier layer, are investigated by backscattering spectrometry, x-ray diffraction, and transmission electron microscopy in conjunction with energy dispersive analyses of x-rays. For all samples, the main reaction products after annealing at 450°C for 15 min are Au7Ga2, and PtGe:As, a PtGe phase that also contains arsenic. The product phases are randomly distributed within a laterally uniform reacted layer when the Pt/Ge/Au contact is covered by a Ta-Si-N layer. Without the Ta-Si-N barrier layer, a small arsenic loss and a Ga-rich phase (probably Gaoxides) on the contact surface are observed after annealing at 450°C. In this case, the surface and contact-semiconductor interface are more faceted than with a Ta-Si-N barrier layer.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 300: Symposium D1 – III-V Electronic and Photonic Device Fabrication and Performance , 1993 , 255
Copyright
Copyright © Materials Research Society 1993

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References

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