Energy Resolution Improvement through Digital Pulse Shape Analysis at CdZnTe-Cross-Strip-Detectors

CdZnTe is a semiconductor material with very good properties for gamma-ray detection. A relatively large band gap of 1.57 eV allows the use at room temperature without any additional cooling. Since holes are nearly immobile compared to electrons in CdZnTe, spectroscopic readout requires special techniques which reduce the depth dependence of the signal. One possibility is to apply an anode pattern which exploits the small pixel effect which induces a signal as the charge cloud is very close to the anode. However, a small current is already induced as the charge cloud travels the bulk. The additional drift current will be accumulated at the charge sensitive preamplifier and influences the base line determination algorithm and results in an additional energy input. We present a simple approach to eliminate the influence of this drift current with the use of pulse shape discrimination implemented in an FPGA of a sampling ADC board. With this algorithm and the known transfer function of the preamplifier a proper depth correction is possible to improve the spectral resolution.