Hopping electronic conduction in metal oxide films and their insulating properties

The author presents results of a study of kinetic electronic phenomena in amorphous tantalum, niobium, and aluminum oxides in different and widely varying environments, and analyzes the effects of composition and structure on the electronic properties of these materials. The experiments were performed on anodic oxide layers of high uniformity with a nearly stoichiometric composition in model capacitor structures prepared using a laboratory process. It has been found that transport processes in such layers are determined by the bulk properties of the oxide dielectric. The experimental results have led to the assumption of a hopping mechanism of conduction in amorphous metal oxide dielectrics. Electron transitions are phonon-assisted jumps of charge carriers between localized states. In a range of relatively high temperatures, charge transport is effected on the energy level corresponding to the maximum density of localized states, whereas, in a lower temperature range, it is near the Fermi level, which accounts for the observed changes in the behavior of oxides with decreasing temperature