Monte-carlo Modeling of Silicon X-ray Detectors

A new 3-D Monte-Carlo code, X-Tracker, was developed to model internal events that occur as X-ray photons are absorbed within Si(Li) detectors. The goal was to model the performance of state-of-the-art detectors, including peak shapes, background and “artifact” peaks found in “clean spectra” from collimated radioactive and other X-ray sources. The model includes the influence of collimation, front contacts, crystal traps or “defects,” passivation walls, dead layers and other boundary effects. Photon fluorescence and scatter and electron effects (including Auger, Photo and Compton electrons) have been included. Monte Carlo and analytical models have been blended to take advantage of both approaches, including the reflection-coefficient concept that explains how charge-carrier collection can be improved with suitable designs of the front interfacial layer. Good agreement has been demonstrated between simulated and real spectra, although there is still some room for improvement. The program has demonstrated its use as a tool for both understanding problems with earlier detector designs, and for improved designs where the need exists for detectors with very clean response functions, in applications such as synchrotron beam lines and polarized XRF spectrometers.