Charge behaviors at surface and interface under ac electric field

Based on the optical observations, the charge behaviors in a planar metal-insulator-metal structure are investigated under ac electric field. Relying on the polarity switching of applied voltage, double charge carriers are injected from both electrodes to the surface layer of insulator or extracted from the insulator to the electrode at the surface/interface region, respectively. These injected charges transport along the surface layer across the electrode gap. EL phenomena would occur due to the radiative recombination of electrons and holes injected. Strongly depending on the applied electric field, two kinds of charge injection mechanisms, i.e., the Richardson-Schottky and the Fowler-Nordheim, are distinguished. The experimental results and theoretical analysis support a new approach to understanding the surface and interfacial phenomena in the field of electrical insulation.