Variations in pulse-height spectnim and pulse timing in CdZnTe pixel array detectors

The signal generated in pixel array detectors for gamma-ray imaging can be strikingly different from the signal seen in single-element detectors. When the pixel size is small compared with the detector thickness, the signal induced in the readout circuit becomes dominated by one charge carrier. If the small pixel is biased positive with respect to the continuous electrode the sensed signal will be due mostly to electron motion while the degrading effects of hole trapping and variation in interaction depth become far less important. To confirm experimentally the predictions of charge transport theory we fabricated CdZnTe test pixels of various sizes. Using a source of alpha radiation we measured the pulse timing properties for electron and hole transport as a function of pixel size. Pulse-height spectra were taken with gamma radiation from """Tc. The results are in good agreement with the model for signal induction.