Progress in Cd 1-x Zn x Te (CZT) Radiation Detectors
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PROGRESS IN Cdl.,Zn1 Te (CZT) RADIATION DETECTORS J. F. Butler, F. P. Doty, B. Apotovsky, S. J. Friesenhahn and C. Lingren Aurora Technologies Corporation 7408 Trade Street San Diego, CA 92121 ABSTRACT Results of a program to improve the performance of Cd 1_•Zn.Te detectors by adjusting growth parameters to achieve low-strain, high purity low defect crystals, investigating surface effect phenomena and contacting methods, and establishing reproducible manufacturing methods are reviewed and discussed. Processing and fabrication methods were developed which are applicable throughout the composition range. Energy spectra for room temperature CdlxZnxTe detectors exhibit resolutions (FWHM) from 2.16 keV at 14 keV to 6.9 keV at 122 keV. An energy resolution of 910 eV at 5.9 keV was achieved at -25 C. Stable ohmic contacts and gamma ray detection for ZnTe are reported for the first time. Applications of Cdl.xZnTe to nuclear medicine and X-ray fluorescence are discussed. New gamma ray imagers using Cd-. 1 Zn.Te detector arrays are described, and imaging data for a 32 x 32 monolithic array of 1 mm 2 elements on a 42mm x 42mm substrate are presented. INTRODUCTION Measurement and analysis of X- and gamma-radiation form the basis of a broad range of beneficial uses for society, from fundamental physical studies to medical diagnostics and industrial applications. In addressing these uses, the radiation detector is an obviously critical component and, in many cases, the prospects of small size, durability, stability and other features make it necessary or highly desirable to use room temperature semiconductor detectors. Approximately two years ago, Aurora Technologies Corporation (ATC) embarked on a research effort to improve the performance of CdTe-type detectors fabricated from crystals grown by a high pressure Bridgman (HPB) technique. It had previously been reported that this approach yielded 7.5-cm diameter, very homogeneous crystals of CdTe that could be used to produce large quantities of at least counting grade detectors1 . Our later efforts were aimed at raising detector performance levels sufficiently to achieve useful energy discrimination over the relevant quantum energy ranges of a number of important applications. The purpose of this paper is to review and discuss the results of these efforts to date. Portions of this work have been previously reported2' 3' ''4 6 . Figure 1 shows a schematic diagram of the HPB growth apparatus we have developed. It employs a vertical Bridgman furnace configuration with crucible, heater, insulation and supporting structure enclosed within a high pressure shell. One advantage of this system of particular relevance to II-VI compounds is its flexibility in the choice of the growth container material; one may, for example, eliminate quartz from the system. Our Mat. Res. Soc. Symp. Proc. Vol. 302. ©1993 Materials Research Society
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furnaces may be used to produce boules of Cd1-,ZnxTe (0 < x
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