A classical method for the accurate measurement of the bulk resistivity and a quantitative separation of bulk and surface leakage currents in semi-insulating CdZnTe radiation detectors is evaluated. We performed an extensive set of experiments on CdZnTe single-crystal test devices to confirm the reliability and reproducibility of the measurements and the validity of the underlying assumptions for data analysis and parameter extraction. The experiments included temperature dependent dual current-voltage measurements on devices with guard electrodes as a function of device thickness, surface preparation, surface passivation, and electrode deposition conditions. We also evaluated the temperature dependence of the bulk resistivity and implemented a general temperature normalization routine to allow a reliable comparison between various crystal samples.
Using the traveling heater method, we have developed commercial CdZnTe (CZT) crystal growth, fabrication, and in-house test technologies for both, photon-starved gamma spectroscopic sensors and high-flux x-ray photon-counting for medical imaging and other applications. We compare the performance of different CZT material types for gamma spectroscopy and for high-flux x-ray imaging. We demonstrate single-threshold photon counting and basic imaging capability of pixelated CZT detectors at the highest x-ray fluxes we could generate in-house, i.e., ∼250 × 106 photons/(mm2 s). We show that the test system can be used for universal, absolute flux calibration of x-ray beams based on an accurate pile-up fitting algorithm. The detectors also perform spectroscopically under high-flux, when tested with energy discriminating electronics. A brief investigation on the effects of leakage, photo, and excess currents including their temporal behavior is also presented. Sub 1% uncorrected single-pixel resolution of the 662 keV 137Cs full energy peak was achieved with the gamma spectroscopy optimized material, fabricated into pixelated sensors.
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