Tunneling current density j(V) for Pb--In--Au alloy junctions and tunnel barrier modeling

Tunnel barriers formed by rf oxidation of Pb--In--Au alloys and consisting largely of In2O3 have been studied by measuring the current density as a function of applied voltage j(V) for voltages up to 1 V. The junctions studied here, which were oxidized on Pb- or photoresist-coated rf cathodes, showed no evidence of a barrier height below about 1 eV. A trapezoidal barrier with a height of at least 1 eV and a thickness equal to that of the oxide film, roughly 6 nm, would have a tunneling current far below that observed for these junctions. Furthermore, the measured j(V) curves were inconsistent with those calculated for a trapezoidal barrier, even for a barrier thickness less than the physical oxide thickness. The j(V) curves were, however, similar to those calculated for tunneling through a Schottky barrier in the indium oxide at the interface with the counterelectrode. Such a barrier, which is also suggested by recent measurements of oxide thickness and junction electrical properties at low voltages, might be expected to form between the metal electrodes and In2O3, which can be a degenerately-doped n-type semiconductor