Trap energy distribution in polymeric insulating materials through surface potential decay method

A model based on surface potential decay (SPD) measurement was developed to study the trap energy distribution of hole-type and electron-type traps in materials by considering two distinct energy levels (i.e., shallow and deep traps) and the detrapping process. An approximated Dirac function δ((E-Em)/kT) was also introduced to obtain a consistent unit of trap density. Besides, the space charge distributions (such as uniform, linear and exponent distribution) in positively and negatively charged materials were also taken into account. In order to verify our proposed model, the different SPD curves of low density polyethylene (LDPE), LDPE/zinc oxide (ZnO) microcomposite and nanocomposite were analyzed. The results show that the proposed model is effective to obtain the trap energy distribution in materials. The SPD curves in positively and negatively charged samples show a fast decay followed by a slow decay, which is agreed with our assumption of shallow and deep traps. Two peaks are clearly observed from the trap energy distribution. The trap energy distributions of hole-type and electron-type traps in these materials are distinct from each other. This implies some essential nature of hole-type and electron-type traps (i.e., intra-chain character for hole-type traps and inter-chain character for electron-type traps). In addition, compared to LDPE and LDPE/ZnO microcompoiste, the decreasing energy level and the increasing trap density of shallow traps as well as the decreasing trap density of deep traps in LDPE/ZnO nanocomposite may be attributed to the effect of the interaction zone surrounding nanoparticles.