Surface-potential decay in insulators with deep traps

Abstract

Surface‐potential decay characteristics of corona‐charged insulators are analyzed theoretically using a theory developed before by Rudenko. It was assumed that the charges are deposited in the surface of the insulator by a short corona pulse and that some amount of charge is instantaneously injected in the bulk of material. An analytical treatment of the standard transport equations in the presence of traps is presented. The model assumed for the traps is one in which they can be characterized by a single trapping time; liberation from traps was neglected, and also it was assumed that the traps are far from fully occupied. Using the theory it was possible to explain the fast decay of surface potential after a negative corona discharge in naphthalene single crystals. The value found for the trap‐modulated mobility at room temperature was 10−8cm2 V−1 s−1 and 110 s for the trapping time used as a parameter. With measurements of thermally stimulated currents, it was possible to find two sets of traps with activation energies of 0.6 and 1.2 eV.