Abstract
Wide bandgap semiconductor materials capable of detecting X-rays and gamma-rays at room temperature without cryogenic cooling have great advantages that include portability and wide-area deployment in nuclear and radiological threat defense. Additional major applications include medical imaging, spectroscopy, and astrophysics. Most current room-temperature ionizing radiation detector devices are fabricated from cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe). Cadmium zinc telluride selenide (CdZnTeSe or CZTS) can be grown with high crystal yield compared to CdTe and CdZnTe. Thus, CZTS has the advantage of lowering the cost of room-temperature nuclear detectors. Thick CdTe-based detectors are prone to the trapping of charge carriers, thus limiting energy resolution and efficiency. A Frisch-Grid configuration helps to solve this problem. This research is focused on optimizing the Frisch-grid configuration for a CZTS detector. The CZTS was grown by traveling heater method. Infrared images of the CZTS matrix largely showed the absence of tellurium inclusions. The resistivity of the CZTS obtained from a current-voltage plot is of the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> Ω.cm. The charge-transport characterized by measuring the electron mobility-lifetime product is 4.7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V. Detector resolution was measured for various Frisch-ring widths. For a 4.8 × 4.9 × 9.7 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> detector, the best Frisch-ring widths were found to be 3-4 mm. A detector resolution of 1.35% full-width-at-half-maximum was obtained for the 3-mm width at -2300 V bias voltage for the 662-keV gamma peak of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs. A resolution of 1.36% was obtained for the 4-mm width at -1800 V applied bias.
Highlights
Semiconductor photonic materials capable of detecting X-rays and gamma-rays at room temperature without cryogenic cooling have great advantages that include portability and wide-area deployment in nuclear and radiological threat defense
In our studies using photo-induced current deep-level transient spectroscopy, we found that Bridgman-grown CZTS showed a high density of the 1.1-eV trap compared to the absence of the 1.1-eV trap in traveling heater method (THM)-grown CZTS [20], [21]
In our chemical passivation studies on one of our recent CZTS (Cd0.9Zn0.1Te0.96Se0.04 grown by THM) using 10% aqueous solution of ammonium fluoride, we found an average of 25% improvement in the resolution of a planar detector (7.00 × 4.65 × 2.70 mm3) for the 59.6-keV gamma line of 241Am at bias voltages in the range −35 V to −200 V [29]
Summary
Semiconductor photonic materials capable of detecting X-rays and gamma-rays at room temperature without cryogenic cooling have great advantages that include portability and wide-area deployment in nuclear and radiological threat defense. Prominent of these wide-bandgap semiconductors are cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe). These materials are prone to low detector yield due to defects that are related to Te inclusions, sub-grain boundary network, precipitates and nonuniform composition [6]–[8]. This in turn leads to a relatively high cost of X-ray and gamma-ray detection devices built from CdTe and CdZnTe materials. A major effort at reducing the defects and increasing the crystal growth yield is to grow CdTe-based materials that have greater uniformity in the crystal structure
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