A space-charge and relaxation-current based method for estimating electron and hole trap energy distribution

Abstract

To estimate arbitrary electron and hole trap energy distribution of cross-linked polyethylene (XLPE), a modified method based on the combination of relaxation current and space charge measurement is proposed. This method is on the premise that homocharges are injected at the shallow depth of dielectrics and then detrap and flow away from electrodes. During depolarization, space charge and relaxation current are measured simultaneously by a specialized pulsed electro-acoustic (PEA) equipment. Furthermore, the decrease rates of positive and negative space charge are separately calculated and the ratio between them are employed to differentiate the contribution of electrons and holes to relaxation current. Thus, the relaxation current can be divided into two components to calculate energy distribution of electron and hole traps. Besides, simulation based on a modified bipolar charge transport model with calculated energy distribution were performed to simulate the dynamics of space charge. The experiment results of XLPE show that more hole traps than electron traps exist at energy levels above 0.86 eV. The energy distribution corroborates the decay pattern of space charge. In addition, the simulation results show the same qualitative characters as experiment results. Therefore, this method could be employed to estimate arbitrary trap energy distribution and the simulation may help give an insight of trap properties as well as space charge dynamics.