The effects of Te precipitates on the performances of CdZnTe nuclear radiation detectors were investigated with
wide X-ray or alpha-particle beams. In these measurements, the degradations in the device performances were correlated
with the areas of high concentrations of Te precipitates aggregated around the crystalline defects or with large-size (>100
μm) individual precipitates. The critical role of the small-size, 1-20 μm in diameter, precipitates was not clearly
established, because of the large size of the particle beams used in prior studies (300-400-μm diameter). Our recent
measurements conducted with a highly collimated, <10 μm, x-ray beam and thin, ~1 mm, CZT crystals proved that even
a single small-size precipitate affects the local charge transport properties in CdZnTe detectors. The next step is to
determine the extent of the potential cumulative effect of randomly distributed Te precipitates on the properties of CZT
detectors. In this work, we report on the modeling of the effects of Te precipitates on measurable characteristics such as
energy resolution, detection efficiency, electron mobility-lifetime product, and others and compare with the experimental
results.
Crystals of the compound semiconductor Cd0.55Mn0.45Te were grown by modified Bridgeman technique. The resulting crystals were transparent, with a deep red color. There were no precipitates visible up to the 1.5μm resolution of the optical transmission microscopy system used. The electrical resistivity was measured to be 1x105Ωcm. The ability to grow large precipitate free crystals makes this system a good candidate for radiation detector elements. Electrical properties must be improved through better control of the concentration of electronically active impurities.
A high-intensity X-ray beam collimated down to a 10-micrometer spot size, available at Brookhaven's National Synchrotron Light Source (NSLS), was employed to perform X-ray mapping to measure the correlation between microscopic defects (precipitates) and variations in the collected charges in long-drift CdZnTe (CZT) detectors. First, we use X-ray diffraction topography (XDT) measurements at the high-energy beamline and IR microscopy to identify the defects distribution and strains in the bulk of CZT crystals. Then, we perform X-ray raster scans of the CZT detectors to measure their responses with 10-micrometer spatial resolution. The brightness of the source allows for good statistics in very short times. Precipitates that were singled out with X-ray scans are locally investigated by applying pulse-shape analysis. The presentation discusses how precipitates affect the device performance.
KEYWORDS: Sensors, Signal detection, X-rays, Shape analysis, Signal attenuation, Clouds, Signal generators, Crystals, Detection and tracking algorithms, Photons
Pulse shape analysis is proved to be a powerful tool to characterize the performance of CdZnTe devices and understand their operating principles. It allows one to investigate the device configurations, electron transport properties, effects governing charge collection, electric-field distributions, signal charge formation, etc. This work describes an application of different techniques based on the pulse shape measurements to characterize pixel, coplanar-grid, and
virtual Frisch-grid devices and understand the electronic properties of CZT material provided by different vendors. We report new results that may explain the performance limits of these devices.
Large-size CZT single crystals of up to 300 cm3 have been grown at Yinnel Tech. These crystals were produced into radiation detectors with excellent performances, leading to enhancements in both energy resolution and detector efficiency.
This study investigates the effectiveness of chemical etchants to remove surface damage caused by mechanical polishing during the fabrication of Cd0.9Zn0.1Te (CZT) nuclear radiation detectors. We evaluate different planar CZT devices fabricated from the same CZT crystals. All detectors used electroless Au for the metal contacts. Different polishing particle sizes ranging from 22.1-μm SiC to 0.05-μm alumina were used, which caused different degrees of surface roughness. Current-voltage measurements and detector testing were used to characterize the effects of surface roughness and etching on the material and detector properties.
Recent progress has been made in the development of the Modified Vertical Bridgman (MVB) technique for the growths of 3-inch diameter CZT crystals for fabrication of x-ray and gamma-ray detectors to operate at room temperature. 40% and 80% of the ingots have the single crystal volumes over 300cm3 and 100 cm3 per ingot respectively. Defects (such as Cd-vacancies, Indium dopants and purity) in CZT have been systematically studied. Detectors fabricated from these CZT ingots showed sharp energy resolution and good uniformity.
Recent results have shown that capacitive Frisch grid structures significantly improve spectroscopic performance of planar CZT detectors especially at higher energies. This paper presents results obtained with larger detectors than those previously reported on. Devices with various aspect ratios and grid length-to-device thickness ratios were fabricated and evaluated. A FWHM energy resolution of approximately 2% at 662 keV was obtained for a device with dimensions of 5 mm x 5 mm x 9.2 mm.
Further progress has been made in the development of the Modified Vertical Bridgman method for the growth of CdZnTe crystals for fabrication of x-ray and gamma-ray detectors to operate at room temperature. Specifically, the diameter of the grown ingots has been increased from 2 to 3 inches. High quality, large volume (up to 6 in3) twin-free single crystals have been produced. Detectors fabricated with this material show sharp energy resolution and good uniformity.
We report on device fabrication and testing of CZT grown by the Modified Vertical Bridgman (MVB) method. Several samples of single-crystal MVB grown CZT were obtained from Yinnel Tech. Both single element devices and 2-dimensional arrays were fabricated. Resistivity and electron mobility-lifetime product were measured, and pulse height spectra were recorded for various isotopic sources. Arrays 5 mm thick and an array 1.13-cm thick were evaluated.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.