Tunnelling conductance of clean and doped Al-I-Pb junctions

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Abstract
The measured conductance of clean and doped Al-I-Pb tunnel junctions has been fitted by a WDB calculation of the conductance by varying the barrier parameters. In undoped junctions the barrier so deduced is highly asymmetric with phi 1 approximately=1.5 eV and phi 2 approximately=4.5 eV. A concentration gradient of fractionally charged negative hydroxyl species incorporated within the barrier during its growth is suggested as the cause of the asymmetry. A thin ( approximately 2.5 AA) high ( approximately 10 eV) barrier, associated with the organic layer, in doped samples satisfactorily reproduces the measured conductances in the calculation but it is surprisingly insensitive to the dopant (acetic acid, lauric acid, phenol and m-cresol).