The X-ray response of CdZnTe

We report the results of a series of X-ray measurements on a 3.1 mm2, 2.5 mm thick CdZnTe detector carried out at the BESSY II and HASYLAB synchrotron radiation facilities. The detector energy response function was found to be linear over the energy range 2.3–100 keV with an average rms non-linearity of 0.6%, consistent with statistics. At room temperature, under full-area illumination, the FWHM energy resolution was 1.6 keV at 5.9 keV rising to 2.9 keV at 59.54 keV. At a reduced detector temperature of −20°C, these fall to 380 and 818 eV FWHM, respectively. Under pencil beam illumination, the measured energy resolution at 2.5 keV was 360 eV FWHM rising to 1558 eV at 100 keV. By best fitting the expected resolution function to the experimental data, we derive a value for the Fano factor of (0.099±0.02). Cooling the detector to −50°C, resulted in no noticeable difference in ΔE above 60 keV, but a 40% reduction at energies <10 keV. At 5.9 keV, the measured resolution under full-area illumination using an 55Fe source was found to be ∼10% broader than that measured at an equivalent energy using a 50 μm diameter pencil beam of synchrotron radiation. However, at 59.54 keV there was no statistical difference between pencil beam and full-area illumination, indicating uniform cystallinity and stoichiometry in the bulk. For energies <50 keV, the measured energy-loss spectra display symmetric photopeaks, becoming increasing tailed at higher energies due to hole trapping. atial uniformity of the detector was investigated by raster scanning a 50×50 μm2, 10 keV monoenergetic X-ray beam across the active area. Apart from a few localized areas, the detector response was found to uniform at the few percent level, consistent with statistics