High-energy X-ray diffraction and topography investigation of CdZnTe |
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Authors: | G A Carini G S Camarda Z Zhong D P Siddons A E Bolotnikov G W Wright B Barber C Arnone R B James |
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Institution: | (1) Brookhaven National Laboratory, 11973 Upton, NY;(2) Department of Electrical Engineering, University of Palermo, 90128 Palermo, Italy;(3) Brookhaven National Laboratory, National Synchrotron Light Source, USA;(4) University of Arizona, 85721 Tucson, AZ |
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Abstract: | High-energy transmission x-ray diffraction techniques have been applied to investigate the crystal quality of CdZnTe (CZT).
CdZnTe has shown excellent performance in hard x-ray and gamma detection; unfortunately, bulk nonuniformities still limit
spectroscopic properties of CZT detectors. Collimated high-energy x-rays, produced by a superconducting wiggler at the National
Synchrotron Light Source’s X17B1 beamline, allow for a nondestructive characterization of thick CZT samples (2–3 mm). In order
to have complete information about the defect distribution and strains in the crystals, two series of experiments have been
performed. First, a monochromatic 67 keV x-ray beam with the size of 300×300 μm2 was used to measure the rocking curves of CZT crystals supplied by different material growers. A raster scan of a few square
centimeter area allowed us to measure the full-width at half-maximum (FWHM) and shift in the peak position across the crystal.
The rocking curve peak position and its FWHM can be correlated with local stoichiometry variations and other local defects.
Typically, the FWHM values ranging from 8.3 arcsec to 14.7 arcsec were measured with the best crystal used in these measurements.
Second, transmission white beam x-ray topography (WBXT) was performed by using a 22 mm×200 μm beam in the energy range of 50 keV to 200 keV. These types of measurements allowed for large area, high-resolution (50 μm) scans of the samples. Usually, this technique is used to visualize growth and process-induced defects, such as dislocations,
twins, domains, inclusions, etc. the difference in contrast shows different parts of the crystal that could not be shown otherwise.
In topography, good contrast is indicative of a high quality of the sample, while blurred gray shows the presence of defects.
Correlation with other techniques (e.g., infrared (IR) mapping and gamma mapping) was also attempted. Our characterization
techniques, which use highly penetrating x-rays, are valid for in-situ measurements, even after electrical contacts have been
formed on the crystal in a working device. Thus, these studies may lead to understanding the effects of the defects on the
device performance and ultimately to improving the quality of CZT material required for device fabrication. It is important
to study crystals from different ingot positions (bottom, center, and top); consequently, more systematic studies involving
scans from center to border are planned. |
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Keywords: | High-energy x-ray diffraction rocking curve topography CZT crystal quality detectors characterization |
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