Gamma Ray Detection with Cd 0.9 Zn 0.1 Te Based Detectors Grown Using a Te Solvent Method
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Gamma Ray Detection with Cd0.9Zn0.1Te Based Detectors Grown Using a Te Solvent Method Sandeep K. Chaudhuri, Kelvin J. Zavalla, Ramesh M. Krishna, and Krishna C. Mandal* Department of Electrical Engineering, 301 Main Street, University of South Carolina, Columbia, SC 29208, U.S.A. ABSTRACT Cd0.9Zn0.1Te (CZT) single crystal has been grown using a tellurium solvent method. Two CZT crystals have been chosen from two different locations of the grown ingot. The two crystals were characterized using infrared transmission (IR) imaging and radiation detectors in planar geometry were fabricated on them. Current-voltage characteristics (I-V) revealed a resistivity of ~8.6×1010 cm for detector A (6.9×6.9×4.8 mm3) and 6.7×1010 cm for detector B 3 (11.5×11.7×2.6 mm ). IR imaging showed a lesser concentration of Te inclusions/precipitates in detector A. The transport properties viz., electron drift-mobility and electron mobility-lifetime product were measured using alpha spectroscopy in these detectors in a planar configuration. Detector A showed better charge transport properties compared to detector B. The superior transport properties of crystal A were reflected in the spectroscopic properties of the detectors. Gamma pulse height measurements using a 241Am isotope revealed an energy resolution of ~5 % for detector A and ~7 % for detector B. A digital spectrometer and a biparametric correction scheme was incorporated to recover the pulse height spectrum of high energy gamma rays (137Cs source) from the effect of poor hole movement. INTRODUCTION Cd0.9Zn0.1Te (CZT), a high Z compound semiconductor material, is highly suitable for room temperature x-/gamma ray detection. Adequate photoelectric absorption cross-section, low leakage current, wide bandgap at room temperature, high density and ease of detector fabrication has made it a very suitable candidate for nuclear radiation detection in the field of homeland security, medical imaging, infrared focal plane array, environmental monitoring etc. [1-3]. However, the performance of large volume CZT detectors is limited by the poor charge transport properties like low drift-mobility and lifetime especially for holes. Macroscopic defects such as cracks and twin/grain boundaries and microstructural defects such as mosaic structures, tilt boundaries, dislocations, point defects, impurities, tellurium inclusions/precipitates lead to the poor charge transport properties in CZT materials [1]. In the present work we have used a tellurium solvent method to grow high quality detector grade Cd0.9Zn0.1Te single crystals. Two crystals have been chosen from two different regions of the grown ingot and detectors were fabricated out of them in planar configuration. The Te inclusions/precipitates was characterized using IR transmission imaging and the performances of the detectors were characterized using alpha and gamma spectroscopy. Electron drift mobility and mobility-lifetime product, e e, have been measured using a time-of-flight technique and alpha ray spectroscopy respectively. Digital spectros
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