Study of the Space Charge Induced by an Electron Beam in an Insulating Target

International audienceA model for the building up of space charge in an insulating target under electron bombardment is proposed. Electron–hole pairs are created during inelastic collisions with the valence band and with the inner shells. The elastic effects are due to interactions with the ionic core potentials. Quasielastic contributions come from the excitation of optical and acoustic phonon modes. When its energy becomes sufficiently low, a charge carrier can polarize its surroundings. The formation of a polaron leads to the self-localization of the carrier (electron or hole). The polarons can diffuse in the target under the influence of the internal field due to the space charge. Along their path, they can encounter polaronic traps. In these sites, the polaron can either be stabilized or recombine. All these effects are taken into account in a Monte Carlo simulation model. The internal field is deduced self-consistently from the space charge by solving the corresponding Poisson equation