Performance limits of a 55-/spl mu/m pixel CdTe detector

In this work, the results from simulation of a CdTe pixel detector with a pixel size of 45 mum and a pitch of 55 mum are presented. Simulation of charge sharing between neighboring pixels has been compared with experimental results obtained by the use of the Medipix2 photon counting chip by means of a unique read-out system developed for the Dear-Mama project. Electrical simulations have been performed using the commercial software package DESSIS (ISETCAD) and combined with the Monte Carlo code GEANT4 to simulate the process of interaction and subsequent charge transport of charges induced by radiation. This allowed the analysis of charge sharing between pixel elements, an important limiting factor in imaging applications. Simulation was compared with experimental results obtained by means of a 1 mm thick CdTe detector. Each of these pixel electrodes was connected to the corresponding readout pixel on the Medipix2 chip, via an indium bump-bond. The backside contact was biased at -100 V, so that the pixel electrodes were collecting electrons. The results obtained imply that using a detector 1 mm thick with a pixel size smaller than 55 mum in single photon counting mode is unrealistic, because such fine spatial resolution cannot be attained in the corresponding image due to charge sharing