Simulation of charge sharing in the Caliste-SO detector

Caliste-SO is CdTe X-ray pixelated detector employed in STIX telescope which is one of the instruments on-board Solar Orbiter mission. In such type of detectors charge sharing between adjacent pixels is expected. The effect can affect measured spectra which requires the development of dedicated method for scientific data processing. In this article, we present simulations of the charge sharing with regard to incoming photon energy. We define two processes causing charge sharing: fluorescence and movement of charge cloud. First type was calculated using Geant4 toolkit to determine the response of the detector. Additionally we prepared dedicated software written in Interactive Data Language (IDL) to calculate instrumental effects: Fano and electronic noise, charge loss and properties of the entrance window. To calculate second type of charge sharing we calculated movement of charge cloud in the crystal using Fick's second law. Our simulation shows that for Caliste-SO detectors charge sharing strongly depends on energy of incoming photon. The fraction of events classified as double counts is nearly 6% for 150 keV photons. Furthermore, we calculated the charge sharing for the Caliste64 detector. For this case our result is confirmed by laboratory measurements.