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Electrical and microstructural characteristics of Ge/Cu ohmic contacts to n-type GaAs

Published online by Cambridge University Press:  31 January 2011

M. O. Aboelfotoh ,
S. Oktyabrsky ,
J. Narayan  and
J. M. Woodall
M. O. Aboelfotoh
Affiliation:
Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695–7907
S. Oktyabrsky
Affiliation:
Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695–7907
J. Narayan
Affiliation:
Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695–7907
J. M. Woodall
Affiliation:
School of Electrical Engineering, Purdue University, West LaFayette, Indiana 47907–1285
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Abstract

It is shown that Cu–Ge alloys prepared by depositing sequentially Cu and Ge layers onto GaAs substrates at room temperature followed by annealing at 400 °C form a low-resistance ohmic contact to n-type GaAs over a wide range of Ge concentration that extends from 15 to 40 at. %. The contacts exhibit a specific contact resistivity of 7 × 10−7 Ω cm2 on n-type GaAs with doping concentrations of 1 × 1017 cm−3. The contact resistivity is unaffected by varying the Ge concentration in the range studied and is not influenced by the deposition sequence of the Cu and Ge layers. Cross-sectional high-resolution transmission electron microscopy results show that the addition of Ge to Cu in this concentration range causes Cu to react only with Ge forming the ξ and ε1–Cu3Ge phases which correlate with the low contact resistivity. The ξ and ε1–Cu3Ge phases have a planar and structurally abrupt interface with the GaAs substrate without any interfacial transition layer. It is suggested that Ge is incorporated into the GaAs as an n-type impurity creating a highly doped n+-GaAs surface layer which is responsible for the ohmic behavior. n-channel GaAs metal-semiconductor field-effect transistors using ohmic contacts formed with the ξ and ε1–Cu3Ge phases demonstrate a higher transconductance compared to devices with AuGeNi contacts.

Type
Articles
Information
Journal of Materials Research , Volume 12 , Issue 9 , September 1997 , pp. 2325 - 2331
Copyright
Copyright © Materials Research Society 1997

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