Models of charge transport in electron-beam irradiated insulators

Charge transport in electron-beam irradiated insulators can be studied with various theoretical models based on different assumptions concerning generation, drift, trapping, and recombination of the charge carriers. In the past, two models have been of particular interest. A first macroscopic approach is based on the concept of a radiation-induced conductivity (RIC) generated by the injected electrons. As opposed to this, the second microscopic scheme utilizes a detailed description of carrier generation and recombination in the insulator. While the macroscopic model requires the information of the RIC, the microscopic approach, resulting in a more complicated set of equations, calls for generation and recombination rates in addition to information about mobility and trapping of the more mobile carriers. Comparisons of numerical results from the two models for open-circuit conditions indicate that charge distributions and locations of charge peak and charge centroid are in fair to good agreement, depending on assumptions made for the main parameters. Further comparisons of the simulation results with experimental data for charge distributions and locations of charge peaks in fluoroethylenepropylene and polyimide show that the macroscopic model, with independently determined values for the RIC, yields good agreement with the experimental data. For the microscopic model, good agreement with experiment can also be achieved with properly chosen values of the partially unknown parameters.