Charge sharing measurements of pixilated CdTe using Medipix-II chip

One important consideration of the design and the operation of pixilated detector is the ratio of the pixel size to the thickness of the detector. When the e-h pairs are generated and the charge drifts toward the pixel electrodes under the influence of the bias field, the charge spread is directly related to the drift time, which strongly depends on the carrier mobility and distance travelled by the carriers. This study has general impact on the design of pixilated detector; however its impact on the design and the operation of pixilated detector coupled to photon counting electronics is more profound. The results imply that designing a Cd(Zn)Te detector with very small pixel size, say 25μm and a detector 1 mm thick, is unrealistic because in reality such intrinsic fine spatial resolution can not be attained in the corresponding image due to charge sharing.