Steady-state conduction in high density polyethylene with field-dependent mobility

Abstract

A theory of steady-state conduction of injected space-charge-limited carriers (SCLCs) into high density polyethylene (HDPE) is presented. Injected carriers are deeply trapped at crystalline-amorphous boundaries before the steady state is reached. At elevated temperatures, they are thermally excited to the conduction band in the crystalline regions, and then hop with field-dependent mobility through defect states of the amorphous regions. A hopping site separation of 2.2 nm, corresponding to 9.4×1019/cm3, yields good agreement with experimental current-field characteristics for fields up to 0.5 MV/cm, in the temperature range 61–85.5 °C. The final current I versus field F and temperature T equation shows that the activation energy of the detrapping and transport processes are additive on a semilog plot of I/T vs 1/T. The total activation energy is 1.15 eV at 0.2 MV/cm, in agreement with others. The steady-state field distributions in the sample are calculated, and are independent of temperature in the above temperature and field ranges. The conditions under which our theory reduces to that of simple SCLC, field-independent mobility theory, and differences in conduction between linear low density polyethylene and HDPE are discussed.