Correlation of interface composition and barrier height for model AuGeNi contacts to GaAs

Waldrop, J. R.; Grant, R. W.
February 1987
Applied Physics Letters;2/2/1987, Vol. 50 Issue 5, p250
Academic Journal
Model contacts to GaAs that include nonalloyed layered structures of Au, Ge, and Ni in various combinations are used to establish a correlation between interface composition and large changes in barrier height [lowercase_phi_synonym]B. The interface Fermi level EiF and chemistry during initial contact formation were investigated by x-ray photoemission spectroscopy; the corresponding [lowercase_phi_synonym]B for the thick contact was obtained by current-voltage (I-V) measurement. The circumstances under which a thin (∼10 Å) Ge layer at the GaAs interface can produce [lowercase_phi_synonym]B =∼0.25–0.4 eV (as measured by I-V) are described. For all model contacts examined a [lowercase_phi_synonym]B range from ∼0.25 to 0.9 eV is observed. This result questions the usual assumption of a relatively fixed [lowercase_phi_synonym]B of ∼0.8 eV for the alloyed AuGeNi contact and offers an alternative explanation for the mechanism of ohmic contact formation. The conditions that define the exceptionally low [lowercase_phi_synonym]B contacts provide a guide for the design of nonalloyed tunnel ohmic contacts.


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