Tunneling conductance of metaloxide junctions

The differential conductance behavior of metal/insulator/metaloxide and metaloxide/insulator/metaloxide tunnel structures has been studied. It is found that because of small Fermi energies of metaloxides a number of universally accepted principles of tunneling spectroscopy of conventional materials cease to be valid. First, the shape of tunneling characteristics of a metaloxide is unusually sensible to barrier parameters: the thickness of the insulating layer and the barrier height. If the barrier height is quite large or the thickness is small the dependence of tunnel conductance on voltage for a metaloxide/insulator/metaloxide structure manifests a zero-bias peak resistance anomaly. On further increasing the height or decreasing the thickness the dependence of conductance σ versus voltage V decreases throughout the entire range of voltages. Second, the parabola-like dependence of σ(V) for a metal/insulator/metaloxide structure calculated for a symmetrical rectangular potential barrier appears not to be symmetrical. Its minimum occurs at a finite voltage. Finally, in contrast to metal/oxide/metal contacts the metaloxide tunnel characteristics calculated in the WKB-approximation differ considerably from the corresponding ones obtained in the sharp boundaries model