Analysis of CZT crystals and detectors grown in russia and the ukraine by high-pressure bridgman methods |
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Authors: | H Hermon M Schieber R B James E Y Lee N Yang A J Antolak D H Morse C Hackett E Tarver N N P Kolesnikov Yu N Ivanov V Komar M S Goorsky H Yoon |
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Affiliation: | (1) Sandia National Laboratories, Livermore, CA;(2) Hebrew University of Jerusalem, Israel;(3) Institute of Solid State Physics, Russian Academy of Sciences, Moscow, Russia;(4) Institute for Single Crystals, National Academy of Science, Kharkov, Ukraine;(5) UCLA, Los Angeles, CA |
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Abstract: | Sandia National Laboratories (SNL) is leading an effort to evaluate vertical high pressure Bridgman (VHPB) Cd1−xZnxTe (CZT) crystals grown in the former Soviet Union (FSU) (Ukraine and Russia), in order to study the parameters limiting the
crystal quality and the radiation detector performance. The stoichiometry of the CZT crystals, with 0.04<x<0.25, has been
determined by methods such as proton-induced x-ray emission (PIXE), x-ray diffraction (XRD), microprobe analysis and laser
ablation ICP mass spectroscopy (LA-ICP/MS). Other methods such as triaxial double crystal x-ray diffraction (TADXRD), infrared
transmission spectroscopy (IR), atomic force microscopy (AFM), thermoelectric emission spectroscopy (TEES) and laser induced
transient charge technique (TCT) were also used to evaluate the material properties. We have measured the zinc distribution
in a CZT ingot along the axial direction and also its homogeneity. The (Cd+Zn)/Te average ratio measured on the Ukraine crystals
was 1.2, compared to the ratio of 0.9–1.06 on the Russian ingots. The IR transmission showed highly decorated grain boundaries
with precipitates and hollow bubbles. Microprobe elemental analysis and LA-ICP/MS showed carbon precipitates in the CZT bulk
and carbon deposits along grain boundaries. The higher concentration of impurities and the imperfect crystallinity lead to
shorter electron and hole lifetimes in the range of 0.5–2 and 0.1 μs, respectively, compared to 3–20 and 1–7 μs measured on
U.S. spectrometer grade CZT detectors. These results are consistent with the lower resistivity and worse crystalline perfection
of these crystals, compared to U.S.-grown CZT. However, recently grown CZT from FSU exhibited better detector performance
and good response to alpha particles. |
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Keywords: | Atomic force microscopy (AFM) Cd1− xZnxTe gamma-ray detectors ICP/MS proton-induced x-ray emission (PIXE) thermoelectric emission spectroscopy (TEES) x-ray diffraction (XRD) |
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