Simulation of the collection properties of CdTe strip detectors

CdTe is an attractive material for X-ray and gamma-ray detectors, but the p oor transport properties of holes affect the performance by introducing a l ow energy tailing in the observed spectra. A possible solution to this prob lem is to optimize the electrode geometry, for example, by reducing the dim ension of the anode with respect to the cathode. In this way, the charge si gnal in the external circuit is mostly due to the electrons moving toward t he anode that is where the weighing field becomes localized. The optimizati on of the electrode geometry can be approached by a numerical analysis as t he problem of charge collection is strictly connected to trapping and detra pping processes, which are difficult to be analytically treated in nonunifo rm electric fields. In this paper, we present a numerical simulator based o n a finite difference numerical method (which follows the weighing field ap proach) and on a Monte-Carlo procedure, which is able to analyze, in two di mensions, the effect of different electrode configurations: single strip, m ultiple strip, a single strip with a lateral extended cathode, and, for com parison, the uniform geometry. The results are analyzed in terms of the map s of the local charge collection efficiency and their histograms, equivalen t to the spectra due to high-energy X-rays.