Unravelling surface traps dominated direct-current surface charging and discharging mechanisms

Abstract

Surface traps on a material have a significant influence on charge transport, further determining charging and discharging of an insulator surface. Here, the parameters of surface traps on epoxy composites are tailored through a variety of surface modification methods, and relationships are established between the surface discharge voltage (V_f) and the surface trap depth (E_t) over a wide E_t range. It is found that the E_t dependence of V_f can be divided into three regions, namely, leakage-current, shallow-trap-dominated, and deep-trap-dominated regions. Numerical analysis reveals that in the leakage-current region, a large surface current degrades the solid material and triggers surface discharge. In the shallow-trap-dominated region, the surface charge dissipation rate exceeds the injection rate, surface charge accumulates and the tangential electric field is distorted as E_t increases, and so V_f decreases with increasing E_t. In the deep-trap-dominated region, charge injection and migration are impeded, causing surface charge to accumulate only near electrodes, the distortion of the central tangential electric field is reduced, and V_f increases with increasing E_t. This work provide a comprehensive understanding of surface trap effects in DC surface charging and discharging, and they should prove useful for further dielectric theory, surface modification techniques, and advanced functional devices.