Space-charge-limited currents and thermoelectret state studies in sisal wax

Abstract

A detailed study of current as a function of voltage coupled with that of the thermoelectret state has been undertaken in sisal wax. Below 65°C, Ohm's law is seen to be followed at low voltages, while at higher voltages space-charge-limited conduction following a power-law dependence of current on voltage has been observed. A complete study of the current as a function of voltage, temperature, and thickness indicates an exponential distribution of trapping states in the band gap which is found to be about 7.38-eV wide. Voltage dependence of the quasi-Fermi energy, E f , has been shown to be consistent with the filling of an exponential trap distribution. The dependence of the initial charge densities on the polarizing field and temperature, and their decay with time have shown that the electret state is due to the localization, in different trapping states, of charges which have a double origin: the injection from the electrodes and a thermally activated production of electron—hole pairs in the bulk. The observed initial positive charge densities on one-sided metallized sisal wax samples correspond to trap densities of the order of 10 12 cm −3.