Growth of detector-grade CZT by Traveling Heater Method (THM): An advancement Page: 3 of 10
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Growth of detector-grade CZT by Traveling Heater Method (THM):
An advancement
U. N. Roy', S. Weiler', J. Stein', M. Groza2, A. Burger, A. E. Bolotnikov3, G. S. Camarda3,
A. Hossain3, G. Yang3 and R. B. James3
1FLIR Radiation Inc., 100 Midland Road, Oak Ridge, TN 37830
2Department of Physics, 1000, 17th Avenue North, Fisk University, Nashville, TN 37208
3Brookhaven National Laboratory, Upton, NY 11793
ABSTRACT
In this present work we report the growth of Cdo.9Zno.1Te doped with In by a modified THM
technique. It has been demonstrated that by controlling the microscopically flat growth interface,
the size distribution and concentration can be drastically reduced in the as-grown ingots. This
results in as-grown detector-grade CZT by the THM technique. The three-dimensional size
distribution and concentrations of Te inclusions/precipitations were studied. The size
distributions of the Te precipitations/inclusions were observed to be below the 10-pm range with
the total concentration less than 105 cm-3. The relatively low value of Te inclusions/precipitations
results in excellent charge transport properties of our as-grown samples. The (pv)e values for
different as-grown samples varied between 6-20 x10-3 cm2/V. The as-grown samples also showed
fairly good detector response with resolution of -1.5%, 2.7% and about 3.8% at 662 keV for
quasi-hemispherical geometry for detector volumes of 0.18 cm3, 1 cm3 and 4.2 cm3, respectively.
INTRODUCTION
In spite of ongoing active research to develop novel room-temperature detector materials,
CdZnTe (CZT) has continued to be the most promising semiconductor material for room-
temperature nuclear detector applications for almost two decades. Presently there is an increasing
demand for larger volume, especially larger thickness (>10 mm) CZT detectors for homeland
security applications for fast and unambiguous nuclide identification. Thicker detectors also
provide sufficient stopping power for higher energy gammas and better standoff detection.
Although the Travelling Heater Method (THM) technique is well established for the growth of
large-volume single crystalline CZT crystals, the main bottleneck until today has been the
requirement for post-growth annealing for detector applications [1, 2]. The THM technique
offers many advantages over melt-growth techniques. The main advantage is the fairly uniform
Zn concentration along the growth direction [3, 4]. The uniform Zn concentration is essential for
good charge transport especially for thick detectors in addition to better yield. As it is well
known that THM is a lower temperature growth process compared to Bridgman (i.e., much
below that the melting point of CZT), advantages of lower growth temperature are less or no
chance of explosion of the growth ampoule, less contamination from the crucible, and less defect
density. Schoenholz et al. [5] reported lower etch pit density for THM-grown CdTe compared to
Bridgman-grown CdTe. They also demonstrated that the defect density reduces drastically in the
grown crystal compared to the seed. Recently Gang et al. [6] demonstrated that Te acts as a
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ROY, U.N.; JAMES, R.; WEILER, S.; STEIN, J.; GROZA, M.; BURGER, A. et al. Growth of detector-grade CZT by Traveling Heater Method (THM): An advancement, article, April 25, 2011; United States. (https://digital.library.unt.edu/ark:/67531/metadc846995/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.