In this paper, we complement our previous work on the study of low-temperature rectifying junctions based on Ag/ZnO Schottky barriers. Diodes characterized by very high I ON / I OFF ratio and ideality factors considerably higher than unity, in disagreement with the thermionic emission model, are modeled with a 2-D finite-element simulator. We could discard tunneling and inhomogeneous barrier-height distribution as sources for this anomalous value. A new interface charge layer model was therefore introduced, which is able to reproduce the electrical behavior in devices with large ideality factors without decreasing the rectifying properties.