Simulation of the collection properties of CdTe strip detectors

CdTe is an attractive material for X-ray and gamma-ray detectors, but the poor transport properties of holes affect the performance by introducing a low energy tailing in the observed spectra. A possible solution to this problem is to optimize the electrode geometry, for example, by reducing the dimension of the anode with respect to the cathode. In this way, the charge signal in the external circuit is mostly due to the electrons moving toward the anode that is where the weighing field becomes localized. The optimization of the electrode geometry can be approached by a numerical analysis as the problem of charge collection is strictly connected to trapping and detrapping processes, which are difficult to be analytically treated in nonuniform electric fields. In this paper, we present a numerical simulator based on a finite difference numerical method (which follows the weighing field approach) and on a Monte-Carlo procedure, which is able to analyze, in two dimensions, the effect of different electrode configurations: single strip, multiple strip, a single strip with a lateral extended cathode, and, for comparison, the uniform geometry. The results are analyzed in terms of the maps of the local charge collection efficiency and their histograms, equivalent to the spectra due to high-energy X-rays.