Numerical estimation of trap depth in polymeric materials using molecular orbital method

摘要

Trap depth in polyethylene was numerically estimated using calculation of molecular orbital method. In polymeric material, electric conduction seems to be strongly affected by the existence of carrier traps. Therefore the estimation of trap depth is one of important factors for electrical characterization of polymeric materials. However, there are not so many examples to estimate the trap depth. Therefore, authors have tried to calculate it assuming a model of energy band structure and electron orbital using molecular orbital method. By the numerical calculation, the trap depths for electrons and holes formed around carbonyl grope in polyethylene were obtained. Since pure polyethylene doesn't have any localized state to capture carriers, a trap site derived from naturally included impurities like carbonyl group may play a role of trap site in polyethylene. On the other hand, in the case of polyimide, which has benzene ring in main chain, the traps are formed on the structure of main chain around the benzene rings. It means that polyimide originally has the traps in main chain. The depths for negative and positive carriers were also numerically.