Polarization Studies of CdZnTe Detectors Using Synchrotron X-Ray Radiation

High densities of impurities and defects lead to severe charge-carrier trapping that can be major issues in assuring the high performance of CZT detectors. For some medical-imaging applications, the typical X-ray flux can be very high. Under such high irradiation conditions, the trapped charge builds up inside the detector affecting its stability. This phenomenon generally is termed the polarization effect. We conducted detailed studies on polarization in CZT crystals employing a highly collimated synchrotron X-ray radiation source available at Brookhaven's National Synchrotron Light Source (NSLS). We were able to induce polarization effects by irradiating specific areas within the detector. These measurements allowed us to make, for the first time, a quantitative comparison between areas where polarization is induced, and the electron- and hole-collection X-ray maps obtained at low flux, where no polarization is induced. We discuss the results of these polarization studies.