Compensation of CdZnTe signals using a twin shaping filter technique

The performance of high Z solid state detectors has been significantly improved over the last decade: one of the most promising materials for X and gamma ray detectors is CdTe/CdZnTe, which has high detection efficiency, no requirement for cooling to cryogenic temperatures, good spectroscopic performances, good time response and imaging capabilities. Unfortunately some important features of semiconductor detectors (pulse height, energy resolution, photopeak efficiency) are affected by the charge collection efficiency: the low mobility of the charge carriers (particularly the holes) and trapping/detrapping phenomena can degrade the CdTe/CdZnTe detectors' performances, depending on the distance between the charge formation position and the collecting electrodes. The deterioration of the spectroscopic performances can be reduced by using either hardware or software techniques. The bi-parametric method herein described is based on a hybrid HW and SW technique that utilizes a twin pulse shaping active filter (one 'slow' and one 'fast') to analyse the same signal. This technique could be particularly suitable for implementation in a readout integrated circuit for multipixel detectors. The experimental results obtained with the application of this biparametric technique with CdZnTe detectors are presented in order to assess the reliability and the efficiency of this compensation method as a function of bias voltage and primary photon energy.