Growth of detector-grade CZT by Traveling Heater Method (THM): An advancement
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Growth of detector-grade CZT by Traveling Heater Method (THM): An advancement U. N. Roy1, S. Weiler1, J. Stein1, M. Groza2, A. Burger2, A. E. Bolotnikov3, G. S. Camarda3, A. Hossain3, G. Yang3 and R. B. James3 1
FLIR Radiation Inc., 100 Midland Road, Oak Ridge, TN 37830 Department of Physics, 1000, 17th Avenue North, Fisk University, Nashville, TN 37208 3 Brookhaven National Laboratory, Upton, NY 11793 2
ABSTRACT In this present work we report the growth of Cd0.9Zn0.1Te 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 of Te inclusions can be drastically reduced in the asgrown ingots. This results in as-grown detector-grade CZT by the THM technique. The threedimensional 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-μm 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 (μ )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 continuous efforts to develop novel room-temperature detector materials, CdZnTe (CZT) remains 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 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 CZT crystals, its main bottleneck until today has been the need 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], which 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 Yang et al. [6] demonstrated that
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