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Compound semiconductors detectors, such as Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CdZnTe), have demonstrated spectroscopic performances for X- and Gamma-ray detection at room temperature operation. Several groups are working on using these detector materials for use in high rate photon counting / energy resolving pixelated detector systems. This paper is focused on the modelling from source to pixel output for the evaluation of the material and the architecture of such detectors. A complete three-dimensional numerical model is presented, coupling the GEANT4 Monte-Carlo modelling of the interaction of incident photons with detector material and computation of applied potential, weighting field and free charge carriers transport including trapping using Finite Elements Method in COMSOL. A 3D mapping of Charge Induction Efficiency (CIE) into the volume of the detector is obtained. The GEANT4 and COMSOL interface has been implemented into Matlab for convenient input into a generic model developed in parallel for the read-out electronics. Simulated detection spectra at pixel ouput are obtained and discussed for various detector thicknesses.