Effects of dislocations and sub-grain boundaries on X-ray response maps of CdZnTe radiation detectors
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Effects of dislocations and sub-grain boundaries on X-ray response maps of CdZnTe radiation detectors A. Hossain1, A. E. Bolotnikov1, G. S. Camarda1, Y. Cui1, R. Gul1, K. Kim1, B. Raghothamachar2, G. Yang1 and R. B. James1 1
Brookhaven National Laboratory, Upton, NY, USA 2 Stony Brook University, Stony Brook, NY, USA
ABSTRACT The imperfect quality of CdZnTe (CZT) crystals for radiation detectors seriously diminishes their suitability for different applications. Dislocations and other dislocationrelated defects, such as sub-grain boundaries and dislocation fields around Te inclusions, engender significant charge losses and, consequently, cause fluctuations in the detector’s output signals, thereby hindering their spectroscopic responses. In this paper, we discuss our results from characterizing CZT material by using a high-spatial-resolution X-ray response mapping system at BNL’s National Synchrotron Light Source. In this paper, we emphasize the roles of these dislocation-related defects and their contributions in degrading the detector’s performance. Specifically, we compare the effects of the subgrain- and coherent twin-boundaries on the X-ray response maps. KEYWORDS: CdZnTe, radiation detectors, dislocations, and crystal defects INTRODUCTION The inadequate quality of today’s CdZnTe (CZT) crystals is the main factor limiting their performance and availability of CZT radiation detectors. Previously, we demonstrated that dislocations and other dislocation-related defects, such as sub-grain boundaries and the dislocation fields around Te inclusions, cause significant charge losses and, consequently, fluctuations in the output signals that obstruct the spectroscopic responses of CZT detectors [1]. In this paper, we present our new experimental results from characterizing CZT material using a high-spatial resolution X-ray mapping system at BNL’s National Synchrotron Light Source. The results emphasize the roles of impurities and secondary phases accumulated by dislocation-related defects in causing such degradation. Specifically, we compare the effects of the sub-grain- and coherent twin-boundaries on the X-ray response maps. Sub-grain boundaries are an important class of defects, in addition to impurities and Te inclusions, which occur in all commercial CZT materials, regardless of the growth techniques or their vendors. Usually, the vendors cannot specify the content of sub-grain boundaries in their crystals when they sell them, because they mainly employ IR screening methods that are inadequate for identifying sub-grain boundaries. The most effective techniques, unavailable to the vendors for routine material screening, are white
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beam X-ray diffraction topography. Chemical etching of crystal surfaces, e.g., Saucedo solution [2], is also helpful to trace out such defects. A large variety of sub-grain boundaries is classifiable by their effects on the device’s performances: Some likely are of little harm, and, in many cases, can be neglected entirely. Our previous measurements indicate that the effects of the b
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