Behavior of Charge Carriers in Organic Insulating Materials

Organic insulating materials have been widely used in electrical and electronic equipments and a large number of papers have been published for the past several decades. However, the behavior of charge carriers in organic insulating polymers is not well understood yet because insulating polymers have complicated physical/chemical structure and also various additives and impurities which strongly affect the behavior of carriers. The understanding of the physics behind the behavior of charge carriers is necessary for the development of high-performance materials and the further improvement of electrical apparatus and cables. In this paper, the author will try to find the physics behind fundamental carrier behavior in organic insulating polymers. I focus on carrier transport, carrier trap (localized state) and carrier injection of polyethylene (PE). Recent band calculation of PE provided useful hints to understand the carrier transport and carrier traps. The physical defects due to disordered chain folding and the chemical defects such as impurities and oxidation byproducts act as carrier traps and strongly affect the carrier transport and injection. The morphology and the molecular motion of a polymer also play an important role in carrier transport. The space charge measurement techniques such as the PEA method enable us to directly observe the behavior of carriers. Their results are very useful to understand what happens in real insulating polymers.