Study of CdTe and CdZnTe detectors for X-ray computed tomography

The application of CdTe and CdZnTe 2D-array detectors for medical X-ray Com puted Tomography (XCT) is investigated. Different metallic electrodes have been deposited on High pressure Bridgman Method CdZnTe and on Traveling Hea ter Method CdTe:Cl. These detectors are exposed to X-rays in the CT irradia tion conditions (E-max = 125 keV, (E) over bar = 70 keV, Phi (x) = 4 x 10(1 0) ph s(-1) cm(-2)) and are characterized experimentally in current mode. H igh dynamic range and fast current decrease after the X-ray beam cut-off ar e required for the application. Detectors performances such as sensitivity and response speed are then studied. The performances achieved are encourag ing: dynamic ranges higher than four decades and current decreases of about three decades in 4ms after X-ray beam cut-off are obtained. Nevertheless, these detectors are still limited by a memory effect that makes them not ye t suitable for XCT. Experimental results are explained by important charge trapping and de-trapping due to the presence of high-level densities. The t rapped carrier space charges may also influence the injection from the elec trodes. Our conclusions are confirmed by experiments at low temperature and by laser time-of-flight measurements. The information we get on the predom inant involved levels are correlated with traditional level studies in orde r to identify them (energy depths, origins) and to overcome the actual CdTe and CdZnTe detectors limitations for XCT. (C) 2001 Elsevier Science B.V. A ll rights reserved.