Injection, transport and trapping of electrons in overlayered insulators

This work is focused on the charging behavior of bulk dielectric sample covered with a surface layer. Indeed, thanks to a flight-drift model of electrons and holes in insulators and an iterative computer simulation, it is possible to understand the charge transport and trapping in bulk insulating samples. However the presence of a surface layer modifies the electrical charging of the whole sample, as previously experimentally shown by other teams. The aim of the present work is to show by simulation and experimental measurements, the influence of an overlayer on the electron and hole injection, drift and trapping, on the secondary electron emission and on the spatial charging of overlayered dielectrics. A special effective layer method is introduced in the model to describe the electron scattering and straggling in the layered sample. The surface leakage currents on the top surface are also taken into account, as well as the effects of the temperature on the trapping-detrapping processes by a Poole-Frenkel like approach. The numerical and experimental results will be presented in the case of a bulk alumina which surface has been modified by femtosecond laser irradiation.