Crystal Growth and Characterization of CdTe and Cd 0.9 Zn 0.1 Te for Nuclear Radiation Detectors
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1038-O04-02
Crystal Growth and Characterization of CdTe and Cd0.9Zn0.1Te for Nuclear Radiation Detectors Krishna C. Mandal, Sung H. Kang, Michael Choi, Alket Mertiri, Gary W Pabst, and Caleb Noblitt EIC Laboratories, Inc., Norwood, MA, 02062 ABSTRACT CdTe and Cd0.9Zn0.1Te (CZT) crystals have been studied extensively at EIC Laboratories for various applications including x- and γ-ray imaging and high energy radiation detectors. The crystals were grown from in-house zone refined ultra pure precursor materials using a vertical Bridgman furnace. The growth process has been monitored, controlled and optimized by a computer simulation and modeling program (MASTRAPP). The grown crystals were thoroughly characterized after cutting wafers from the ingots and processing by chemomechanical polishing. The infrared (IR) transmission images of the processed CdTe and CZT crystals showed an average Te inclusion size of ~10 μm for CdTe crystals and ~8 μm for CZT crystals. The etch pit density was ≤ 5×104 cm-2 for CdTe and ≤ 3×104 cm-2 for CZT. Various planar and Frisch collar detectors were fabricated and evaluated. From the current-voltage measurements, the electrical resistivity was calculated to be ~ 1.5×1010 Ω·cm for CdTe and 25×1011 Ω·cm for CZT. The Hecht analysis of electron and hole mobility-lifetime products (μτe and μτh) showed μτe=2×10-3 cm2/V (μτh=8×10-5 cm2/V) and μτe=3-6×10-3 cm2/V (μτh=4-6×10-5 cm2/V) for CdTe and CZT, respectively. Final assessments of the detector performance have been carried out using 241Am (60 keV) and 137Cs (662 keV) energy sources and the results are presented in this paper.
INTRODUCTION CdTe and CdxZn1-xTe (cadmium zinc telluride, CZT) are the most attractive materials for room temperature γ-ray and X-ray spectroscopy. Among many candidate materials for γ-ray detectors, CdTe and CZT are the most promising due to their room temperature operation, high average atomic number (Z∼50), wide bandgap (≥1.5 eV at 300K) and high density (∼5.8 g/cm3) [1]. Currently used low bandgap Si and Ge detectors can only work efficiently at liquid-nitrogen temperature, which is not suitable for portable room temperature applications. Traditional scintillation detectors connected to photomultiplier tubes are not capable of providing resolutions as high as CdTe and CZT detectors because the energy required for generating one electron-hole pair in scintillator crystals (~50 eV) is much larger than that required for CdTe and CZT (4-5 eV). There have been increasing demands in high-resolution detection and identification of individual isotopes in real-time in various environments, especially for Homeland security applications. In addition, there has been active research in CZT detectors that has shown spectral performance improvement using novel single carrier detector designs such as Frisch collar [2, 3], small pixel [4] and coplanar grid [5]. Due to these advantages, CdTe and CZT have been the primary semiconductor materials for room temperature X-ray and γ-ray detectors in medical imaging, infrared focal plane arra
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