The study of interface states in ZnO varistors by injection pulse width dependence of transient response

The injection pulse width dependence of transient response was studied to i nvestigate the interface states in the Bi- and Pr-type ZnO varistors in mor e detail using isothermal capacitance transient spectroscopy (ICTS). Althou gh the interface states have been considered to be distributed monoenergeti cally or discretely, two or three different interface states of the emissio n process were confirmed by varying the injection pulse width at each measu rement temperature. For both types of ZnO varistors, the ICTS spectrum over lapping of the interface states consists of two transient responses: the pr eviously reported trap (Trap 1) and Trap 0 which has a faster emission proc ess than Trap 1. For only Bi-type ZnO, Trap 2 which has a slower emission p rocess, was successfully detected at the longer region of the injection pul se widths t(w) from 1 s to 100 s. This result suggests that the formation o f Trap 2 can he attributed to the existence of Bi2O3. In the case of the ap plication of ICTS for the interface states in ZnO varistors, it is necessar y to select the optimal injection pulse width which takes into account the emission processes at each measurement temperature.