Appearance of a Tunneling Spectrum Peak by Electrical Breakdown of Tunneling Junction

Inelastic electron tunneling spectra of metal/AlO _x/metal junctions were measured at 77 K. For as-made samples up to 0.3 V, the only observable peak occurred near 0.04 V. After electrical breakdown induced both by a ramped voltage stress and by a constant voltage stress, a peak appeared near 0.09 V. It is thought that a conduction level, which is about 0.09 eV higher than the Fermi level, was created in AlO_x by the electrical breakdown. The breakdown is not thought to be due to a simple short circuit caused by a pinhole or the like.