Poole-Frenkel Effect and Schottky Effect in Metal-Insulator-Metal Systems

Existing experimental data on the bulk conductivity of ${\mathrm{Ta}}_{2}$${\mathrm{O}}_{5}$ and SiO films are shown to be consistent with the Schottky effect rather than the Poole-Frenkel effect. A discussion of the physical properties of vacuum-deposited insulators has led to a simple model in which the insulator is proposed to contain neutral traps and donor centers. This model is shown to resolve the above-mentioned "anomalous" Poole-Frenkel effect. Other simple models are discussed, but they do not exhibit the anomalous Poole-Frenkel effect.