Behavior of Local Charge-Trapping Sites in La2O3–Al2O3 Composite Films under Constant Voltage Stress

Abstract

We have investigated the behavior of local charge-trapping sites in La2O3–Al2O3 composite films under electrical stress by observing local leakage current by conductive atomic force microscopy (C-AFM). The total area of leakage spots was observed to increase in current images obtained when repeating C-AFM observation at a constant substrate voltage. This phenomenon can be explained by the local trapping of holes in the film in which the Fowler–Nordheim tunneling current becomes predominant. On the other hand, in the area without leakage spots, average leakage current gradually decreases, due to the electron trapping in the film. The present C-AFM observation clearly reveals different behaviors of trapping sites for electrons and holes; the trapped holes are more easily detrapped than the electrons, and the number of electron-trapping sites is more effectively reduced by additional thermal oxidation than the number of holes.