Model of plasmon decay for electron cascade simulation

A dominant energy loss mechanism for electrons in radiation cascades is the excitation of plasmons. Once created, plasmons eventually decay through interband transitions, leading to the production of additional charge carriers that are responsible for much of the signal measured by the detector. The cross-sections for exciting plasmons and charge carrier pairs follow from the material's dielectric function, The energy distribution of the resulting secondary particles can be obtained from the one-electron orbitals in the random phase approximation (RPA). We apply this method to a nearly free electron crystal for plasmon decays. A Monte Carlo simulation of the resulting decay cascade is carried out for material parameters appropriate to silicon, using the Callaway-Tosatti dielectric function for cascading electrons and holes. Parameters that characterize the detector performance (mean energy to produce a charge carrier pair and the Fano factor) are determined, and are found to be sensitive to the low-energy electronic structure. (c) 2007 Published by Elsevier B.V.