Correlation between nuclear response and defects in CZT Page: 1 of 11
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Correlation between nuclear response and defects in CZT
H. Hermon, M. Schieber *ab, R.B. James b, E. Leeb, E. Cross, t ,
M. Goorsky c, T. Lam c, T.E. Schlesinger d, M. Greaves d 0 Z 0
a The Hebrew University of Jerusalem, Jerusalem 91904, Israel
b Sandia National Laboratories, Livermore, CA 94550
University of California - Los Angeles, Los Angeles, CA 90024 mom
d Carnegie Mellon University, Dept. of Elec. Eng., Pittsburgh, PA15213
Vertical high pressure Bridgman (VHPB) was considered until now to be the most successful crystal growth method to
produce Cd.,ZnxTe (CZT), (0.04 < x < 0.24), for X- and gamma-ray detector crystals. Recently Horizontal Bridgman (HB)
Cd..Zn.Te crystals produced by IMARAD Co. have also been successfully fabricated into nuclear spectroscopic radiation
detectors. In view of our database of many years' study of the electrical properties of VHPB CZT grown and obtained from
various sources, we also studied the HB CZT crystals in order to compare the defects present in both different kinds of
crystals grown by different methods. The VHB-grown samples were examined using thermoelectric emission spectroscopy
(TEES), X- and gamma ray spectroscopy and laser induced transient charge technique (TCT). The surface and the bulk
crystalline homogeneity were mapped using triaxial double crystal x-ray diffraction (TADXRD) and infrared transmission
spectroscopy (IR). We have found a correlation between crystallinity, IR transmission microstructure and trapping times.
Spectrometer grade VHPB CZT crystals exhibit trapping times of 20 js for electrons and 7 ps for holes, however, regions,
which were opaque to IR transmission, had trapping times shorter by one order of magnitude. The trapping times of HB
CZT for electrons, were 10-15 s. A similar trend has'been observed on VHPB CZT crystals with poor crystallinity. The
HB CZT crystals that we measured in this study had a crystallinity that was inferior to that of the best spectroscopic grade
Keywords: Cadmium Zinc Telluride (CZT), X-ray diffraction (XRD), Horizontal Bridgman (RB), vertical high pressure
Bridgman (VHPB), IR transmission, and transient charge technique (TCT).
Cd ,Zn.Te crystals, with 0.05<x<0.4, are leading materials for room-temperature operating radiation detector applications
[1-5]. Due to the addition of Zn, CZT has a larger energy gap than CdTe and therefore has some distinct advantages over
CdTe by having a higher value of bulk resistivity, lower dark current and reduced electronic noise. Crystal growth of CZT
has been performed by various methods, however until recently, it is performed mainly by a vertical high-pressure -"
Bridgman (VHPB) process for producing of gamma-ray detectors. Indeed, recently, ambient pressure horizontal Bridgman
(HB) crystals became commercially available, and spectrometric grade detector were fabricated and tested by Sandia
National Laboratories. A large number of papers were published by the Sandia group to characterize the various VHPB
grown CZT crystals produced commercially in the US and in parallel , CZT crystals grown in Russia [6-11] and in the
Ukraine were also evaluated [6,10].
Better understanding of the growth parameters is a must in order to improve the material quality. Therefore, the
opportunities to study in parallel the VHPB and the HB crystals offer an excellent occasion to compare both types of crystal
growth process. It is known that defects are much less common in spectrometer grade CZT detectors. If the spectrometric
grade is of lower quality it is often be due to microstructural defects [8, 11-13]. These defects are typically generated during
the crystal growth process, although the fabrication steps can also introduce defects.
The present paper will show here our first results obtained on HB CZT using X-ray diffraction, XRD, which show the
Zn content Low temperature photoluminescence, PL, and Triaxial XRD, TAD-XRD, and XRD topography will also be
shown. Alpha particle spectroscopy is one of the most common methods used to evaluate the electrical properties of wide
Correspondence: Email: schieberavms.hui.ac.il Phone: +972-2-6584364; FAX +972-2-5663878
Part of the SPIE Conference on Hard X-Ray. Gamma-Ray, and Neutron Detector Physics
138 Denve. Colorado " Ju'
SPIE Vol. 3768 " 0277-786/99/S1O00
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Hermon, H.; Schieber, M.; James, R. B.; Lee, E.; Cross, E.; Goorsky, M. et al. Correlation between nuclear response and defects in CZT, article, July 19, 1999; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc709667/m1/1/: accessed March 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.