Trap Distribution Effects on Time-Dependent Radiation Induced Conductivity

When charge is embedded into Highly Disordered Insulating Materials (HDIM), charge transport can be insufficient to dissipate stored charge and to mitigate the resulting potential differences. If the potential differences become great enough, arcing can occur and create many deleterious issues for applications such as spacecraft or plasma chambers. The charge movement, and hence dissipation, can be increased by radiation induced conductivity (RIC), where incident radiation imparts energy into a material to excite electrons from the valence band and trapped states into the conduction band and back. Hence, energy distributions of trap states are highly relevant to understand the effects of temperature and dose rate on the equilibrium and time-dependent behavior of RIC. Using a dual-defect model for time-dependent RIC, the increased conductivity during irradiation has been modelled as a charging capacitor, while the delayed RIC has been modeled as a diffusion-like hyperbolic decay. The rise and decay functions share the same equilibrium values, and each has both slower and faster contributions from deep and shallow trap distributions, respectively; this is modeled with seven fitting parameters for a continuous time-dependent fit across RIC datasets with multiple square-pulsed dose rates. Recent analysis of data sets for thermoplastic low-density polyethylene (LDPE) over approximately 100 K to 350 K and 0.1 mGy/s to 100 mGy/s dose rates is compared to previous analysis of similar thermoset plastic polyimide (PI or Kapton HNTM) data sets. These materials are examples of different trap distribution densities and energy dependencies, which have been predicted to have markedly different theoretical responses. Measured dependencies of the fitting parameters for the two prototypical materials on temperature and dose rate are compared to the theoretical predictions.