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Oak Ridge, TN, United States

Xu L.,Northwestern Polytechnical University | Xu L.,Brookhaven National Laboratory | Jie W.,Northwestern Polytechnical University | Bolotnikov A.E.,Brookhaven National Laboratory | And 12 more authors.
Journal of Crystal Growth | Year: 2012

We analyzed two CZT crystals cut from as-grown CdZnTe (CZT) ingots, the only difference between them being the rate of cooling after the crystal growth process. Using White Beam X-ray Diffraction Topography (WBXDT) and Infrared (IR) Transmission Microscopy, we identified and quantified the extended defects, e.g., Te inclusions, dislocations, and sub-grain boundaries. The effects of cooling rate on the size distribution and concentration were studied. The WBXDT and IR images of the fast-cooled crystal revealed very high density of dislocations and sub-grain boundaries, crisscrossing throughout its entire volume, extending from deep inside almost to the surface. In addition, IR analyses showed that the concentration of Te inclusions in the fast-cooled crystal (10 6 cm -3) was higher than that in the slow-cooled one (10 5 cm -3). For the latter, both the WBXDT and the IR images were bright and clear with low concentration of defects. We concluded that slow cooling rate can greatly reduce the number of Te inclusions and inclusion-decorated extended defects in as-grown CZT ingots. © 2012 Elsevier B.V.


Roy U.N.,FLIR Radiation Inc. | Weiler S.,FLIR Radiation Inc. | Stein J.,FLIR Radiation Inc. | Groza M.,Fisk University | And 6 more authors.
Materials Research Society Symposium Proceedings | Year: 2012

In this present work we report the growth of Cd 0.9Zn 0.1 Te 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 three-dimensional 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-μ 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 (μτ)ε values for different as-grown samples varied between 6-20 × 10 -3 cm 2/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 cm 3, 1 cm 3 and 4.2 cm 3, respectively. © 2011 Materials Research Society.


Roy U.N.,FLIR Radiation Inc. | Weiler S.,FLIR Radiation Inc. | Stein J.,FLIR Radiation Inc. | Hossain A.,Brookhaven National Laboratory | And 3 more authors.
Journal of Crystal Growth | Year: 2011

The concentration and size distribution of Te inclusions/precipitates in CZT are key factors in a devices performance. High concentrations can degrade the performance drastically, especially for long drift-length devices (more than about 10-mm thick). Here, we extend our previous findings on the concentration and size distribution of Te inclusions/precipitates in CZT wafers grown by the THM technique, by considering the rate of cooling of the ingots. We measured their distribution along the diameter of the wafers in a conventional slow-cooled and a fast-cooled ingot. The overall average concentration of Te inclusions/precipitates for the slow-cooled sample was less than 1×10 5 cm -3, attesting to their suitability for fabricating thick radiation-detection devices. © 2011 Elsevier B.V.


Roy U.N.,FLIR Radiation Inc. | Weiler S.,FLIR Radiation Inc. | Stein J.,FLIR Radiation Inc. | Cui Y.,Fisk University | And 4 more authors.
Journal of Crystal Growth | Year: 2012

We have employed photoluminescence mapping at room temperature of detector grade CZT grown by modified Traveling Heater Method (THM) technique and estimated the spatial variation of Zn composition. The composition was found to be fairly uniform over the major portion of the ingot length except near the conical part of the ingot and the upper part of the ingot. Unlike Bridgman growth technique, no detectable striations were observed. The composition was within ±0.3% over the length little more than 4 cm of the ingot. The growth interface revealed from the composition mapping was found to be reasonably flat. © 2012 Elsevier B.V.


Roy U.N.,FLIR Radiation Inc. | Weiler S.,FLIR Radiation Inc. | Stein J.,FLIR Radiation Inc. | Groza M.,Fisk University | And 4 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

CdZnTe, commonly known as CZT is the material of paramount importance for hard X-ray and gamma ray spectroscopy and imaging applications at room temperature. Over the years, the quality of CZT crystals and its charge transport properties has improved significantly making it an attractive detector material especially for homeland security applications. The applications for homeland security demand large and thick detectors to provide a sufficient stopping power for fast detection of high energy gamma photons. In this present report we have grown two inch diameter CZT by Traveling heater method (THM) technique. The as-grown crystals were characterized through photoluminescence (PL) mapping for composition uniformity, growth interface study, Te precipitations/inclusions studies. In order to evaluate our as-grown samples, charge transport characteristics have been studied for thick samples up to ~16mm thick. It has been demonstrated that by controlling the growth interface, visualization of large and thick (~16mm thick) detectors with fairly good response is possible from as-grown CZT detectors grown by THM technique. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

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