Mr. Wei Qiu Profile

Wei Qiu

at Univ of Florida

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Proceedings Article | 17 September 2009 Paper

Bismuth tri-iodide radiation detector development

Azaree Lintereur, Wei Qiu, Juan Nino, James Baciak

Proceedings Volume 7449, 74491M (2009) https://doi.org/10.1117/12.825037

KEYWORDS: Crystals, Sensors, Spectroscopy, Gamma radiation, Electrodes, Single crystal X-ray diffraction, Bismuth, Palladium, Compound semiconductors, Gold

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Bismuth tri-iodide (BiI₃), a wide band-gap semiconductor, demonstrates many of the material properties necessary for high resolution room temperature gamma-ray spectroscopy. These material properties include high density, large bandgap, and high atomic number. The theoretical intrinsic photopeak efficiency of BiI₃ is approximately 2-3 times higher than CdZnTe over the range of 200-3000 keV. BiI₃ has a theoretical intrinsic photopeak efficiency of 19% at 662 keV, compared to CdZnTe which has a theoretical intrinsic photopeak efficiency of 13% at 662 keV. A modified vertical Bridgman growth method is being used to grow large, greater than 100 mm³, single BiI₃ crystals. Growth parameter optimization has demonstrated that single crystals can be obtained with temperature gradients of 10°/cm or 15o/cm and a growth rate of 0.5 mm/hr, or with a temperature gradient of 10o/cm and a growth rate of 1 mm/hr. Polycrystalline material results from all other growth parameter combinations. X-ray diffraction spectra are used to determine if the crystals are single crystals or polycrystalline. UV-VIS spectra analysis has revealed that the band-gap of BiI₃ is 1.72 eV. The resistivity of the crystals has been determined by generating I-V curves to be on the order of 10⁸-10⁹ Ω-cm. Zone refining is being performed to increase the purity of the starting material and the resistivity of the crystals. Detectors have been fabricated with both gold and palladium electrodes.

Proceedings Article | 17 April 2008 Paper

Iodine based compound semiconductors for room temperature gamma-ray spectroscopy

Azaree Lintereur, Wei Qiu, Juan Nino, James Baciak

Proceedings Volume 6945, 694503 (2008) https://doi.org/10.1117/12.777402

KEYWORDS: Crystals, Spectroscopy, Gamma radiation, Sensors, Electrodes, Semiconductors, Compound semiconductors, Iodine, Polarization, Single crystal X-ray diffraction

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Iodine-based compound semiconductors may allow one to build a portable gamma-ray spectrometer with improved efficiency and energy resolution compared to many other portable spectrometer devices. Iodine-based semiconductors have a wide band gap that allows these detectors to operate without any cooling mechanism. Bismuth iodide (BiI₃), lead iodide (PbI₂) and mercuric iodide (HgI₂) have theoretical gamma-ray detection efficiencies approximately 2-3 times higher than CdZnTe, the current compound semiconductor material proposed for use in several homeland/national security applications, over the range of 200-3000 keV. At 662 keV, BiI₃, HgI₂ and PbI₂ have theoretical intrinsic photopeak efficiencies of 16.8%, 19.3% and 19.9%, respectively, while CdZnTe has a photopeak efficiency of 9.03%. In addition, gamma-ray spectrometers made from iodine-based compound semiconductor materials have demonstrated energy resolutions (FWHM) less than 2% at 662 keV. A 2% FWHM represents a significant improvement over many of today's scintillator-based radiation detectors used for homeland/national security purposes. We present some fundamental challenges in working with iodine-based semiconductors, including crystal growth issues and properties of the materials limiting radiation detector size, and the need for advanced electrode designs. Finally, we present elementary measurements illustrating the detection capabilities of iodine-based compound semiconductor materials.

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