Investigation of the energy resolution and charge collection efficiency of Cd(Zn)Te detectors with three electrodes

Radiation Monitoring Devices, Inc., has recently investigated Cd(Zn)Te detector with three electrodes. Planar devices were refabricated as three-electrode devices after recording pulse height spectra. From the spectroscopy measurements at room temperature, photon energy resolutions of 8.3% and 3.5% FWHM were obtained, without noticeable loss of the detector efficiency, with the "three-electrode detector" for gamma ray energies of 122 and 662 keV, respectively, while no discernable full energy peaks were apparent with the planar detectors. The full contact cathode was grounded while two different bias voltages were applied to each anode electrode, even though the induced signal was collected only from the center anode. By investigation of the real and weighting electric field of the detector, the possible reasons for the improved spectra with the three-electrode detector were determined. The strong real electric field around the two anodes very likely enhances the created charge velocity and results in increasing the possibility to induce full charge collection. From additional measurements with increased differences between two bias voltages applied to the anodes, the effects of the strong real electric field on the improved energy spectrum have been confirmed.