On the potential barrier shape in Al–Al2O3–Al tunnel junctions

Abstract

In the conventional theoretical model for the tunnel current through thin Al2O3-layers sandwiched between metal electrodes a potential barrier of convex curvature is assumed. The convex curvature of the barrier is caused by the image potential. However, in this paper it will be shown, by means of the logarithmic derivative of the tunnel current, that a potential barrier of concave curvature leads to noticeably better agreement with experimental data than the convex barrier. It is suggested that a large positive ionic space-charge in the Al2O3-layer causes the concave curvature of the potential barrier.