High performance CZT grown at accelerated growth rates using the Traveling Heater Method. (#4120)
J. MacKenzie1, F. J. Kumar1, P. Wang1, L. Burgess1
1 Redlen Technologies, Saanichton, British Columbia, Canada
75 mm diameter, spectroscopic grade CdZnTe (CZT) crystal boules were grown using the Traveling Heater Method (THM) at Redlen Technologies at rates up to 24 mm/day. It was found that CZT can be grown at up to 16 mm/day without compromising single crystal yield or performance. Contactless resistivity measurements on the CZT wafers show a very high level of uniformity and an average resistivity of 1.5x1010 ohm-cm (as grown). In terms of inclusion sizes/distributions, the fast grown CZT boules showed no difference from those grown using baseline conditions. Finally, the spectroscopic performance of the fast-grown material is identical to its counterpart grown using a fixed translation rate of 6 mm/day.
Keywords: THM, CZT, accelerated growth
Reduction of secondary phases in as-grown detector grade CdZnTe via accelerated crucible rotation (#3865)
J. J. McCoy1, S. K. Swain1, M. S. Divecha2, J. J. Derby2, K. G. Lynn1, 3
1 Washington State University, Center for Materials Research, Pullman, Washington, United States of America
With its high energy efficiency, high stopping power, and ambient operability, Cadmium Zinc Telluride (CZT) is advantageous as a solid state radiation detector material. However, the occurrence of second phase defects greatly hinders its effectiveness by inhibiting charge carrier transport. Second phase defects, generally Te inclusions, act as trapping and scattering sites for charge carriers by distorting electric field lines which results in low mobility lifetimes products. This effect becomes most pronounced in thick detectors required for homeland security applications. The formation of inclusions in CZT crystal growth is attributed to constitutional undercooling at the solid liquid interface from inhomogeneity in solute distributions. Here we demonstrate that by promoting fluid flow via accelerated crucible rotation (ACRT) during vertical Bridgman growth of CZT we can reduce constitutional undercooling thereby controlling and minimizing inclusion content. Our results demonstrate the effectiveness of ACRT for predictably and significantly reducing second phase content in melt grown CZT without post growth processing.
Keywords: CdZnTe, Bridgman, ACRT
Single-crystal ingot growth of CdZnTe for detector applications (#1559)
T. Wang1, F. Yang1, B. Zhou1, L. Yin1, M. Wang2, N. Jia2, S. Xi2, G. Zha1, W. Jie1
1 Nortwestern Polytechnical University, State Key Lab of Solidification Processing, Xi'an, China
The development of CdZnTe (CZT) detector suffers from the high cost caused by the very low yield of CZT crystal. Polycrystalline is one of the main problems, where grains, twins are commonly observed. In this work, we report our recent effort on growth of single-crystal ingot of CZT by using Bridgman method.
Accelerated Crucible Rotation Technique (ACRT) was introduced. The influence of parameters on the constitutional supercooling was discussed. By optimizing the rotation rate, the accelerated speed, and the waveforms, the shape of growth interface was determined to be convex. Combing the design of furnace structure, the heat conduction and convection distribution are optimized, and thus the interface stability was improved.
Ingots with diameter of 2inch and 4inch with nearly 100% single crystalline part were reproducibly obtained. Wafers of 40*40*5 mm3 and 20*20*15 mm3 were cut from the ingots. The crystallinity was found greatly enhanced, where the FWHM of rocking curve was determined to be 11 arcs, and the density of dislocation etch pit was lower than 1E4. The distribution of composition and defects was measured by using EPMA and PL methods. Good uniformity was shown, where the response of pixelated detectors also proved that. The results indicate that single crystal ingot can not only increase the yield but also improve the crystallinity and the detector performance.
Keywords: CdZnTe; Crystal Growth; Single Crystal Ingot
Study of Compositional Homogeniety and Trace Elements in Cd(Zn,Mn)Te and CdTeSe Crystals (#2157)
A. Hossain1, A. E. Bolotnikov1, G. S. Camarda1, R. Gul2, U. N. Roy1, G. Yang1, R. B. James3
1 Brookhaven National Laboratory, Upton, New York, United States of America
We investigated the elemental distribution and extended defects in CdTe-based crystals with Zn, Mn or Se as the third element in a tertiary compound. Reduction of the bulk defects is vital to the fabrication of high-quality large-volume detectors as they have detrimental effects on detector performance. In this work, we obtained high spatial resolution X-ray fluorescence maps of the compositional elements, as well as the doping elements to determine elemental distributions along both the growth and radial directions of the crystals. We revealed various extended defects in Bridgman and THM grown crystals by exploiting selective chemical etching method and evaluating areal densities and distributions of the etch pits associated with dislocations and other crystallographic defects using IR transmission microscopy and scanning electron microscopy (SEM), combined with energy-dispersive x-ray spectroscopy (EDS). We conducted comparison studies between the samples and correlated the results with detector response measurements to understand the influence of the material properties on the detector performance
Keywords: CdZnTe, X-ray Fluorescence