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7 (See color insert.) (a) Cross section of a typical 50 mm diameter CdZnTe ingot and (b) the matching orientation map measured by EBSD.
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CdTe and CdZnTe semiconductor detectors are solid-state devices that provide direct conversion of the absorbed gamma-ray energy into an electronic signal. Many of the advantages of these detectors for medical applications stem from this inherent energy discrimination and photon-counting capability. In addition, the high radiation stopping power and...
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Control loading devices are currently certified on the basis of tests on their mechanical properties, the criteria for these properties are not related to humans' ability to discriminate these properties. We propose the Objective Inceptor Cueing Test, a new design for control loading device evaluation based on humans' haptic percept limits (the Jus...
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The basic principle of operation of an X-ray detector is described through the X-ray interactions with the photoconductor, the ionization energy, and signal formulation mechanisms in photoconductive radiation detectors. Typical X-ray radiation detector materials and structures are also described. The X-ray detectors are classified based on their applications. The spectroscopic detector operation is explained, and its energy resolution is discussed. Flat panel X-ray imagers (FPXIs) are described in detail due to their extensive use in imaging, especially, in medical X-ray imaging. The materials for direct conversion detectors (the absorbed X-ray photons directly create charge carriers in the photoconductor) and various image read-out devices (e.g., a-Si:H TFT and CMOS active-matrix technologies) are discussed. The imaging performance of FPXIs critically depends on the photoconductor material used in the X-ray detector. This chapter discusses the effects of charge carrier transport properties on the imaging performances such as X-ray sensitivity, resolution in terms of modulation transfer function, detective quantum efficiency, image lag, and ghosting. A brief introduction to the X-ray interaction position sensitive semiconductor detector structures and the effects of small pixels on charge collection and resolution are described in this chapter.KeywordsActive-Matrix ArraysCharge collection efficiencyDetective quantum efficiencyDirect conversion X-ray imaging detectorElectronic noiseFlat-panel X-ray imagerHecht equationImage lag and ghostingIonization energyModulation transfer functionPixelated detectorsPlanar and Co-planar detectorsPosition Sensitive Semiconductor DetectorsRadiation detectorsShockley-Ramo’s theoremSmall pixel effectSpatial resolutionX-ray interactions with photoconductorX-ray photoconductorsX-ray sensitivityX-ray spectroscopic detectors
A two-step growth process of CdZnTe(001) epilayers on GaAs(001) substrates by Close Spaced Sublimation (CSS) is proposed. The first step, or a so-called pre-growth at low temperature of 350 °C generates more compact nucleation layer than the second step growth at 430 °C, which is more efficient for accelerating grain coalescence and annihilation of defect. Both the double crystal X-ray rocking curve (DCXRC) and the photoluminescence (PL) results prove that CdZnTe film with the best crystalline quality is obtained with the combination of the first step growth at 350 °C and the second growth at 430 °C. Increasing the second step growth temperature from 430 °C to 530 °C and 600 °C deteriorate films crystalline quality due to the increase in thermal stress and Zn content. Current-voltage (IV) measurement and alpha-particle response test indicate that better crystalline quality in CZT film leads to both higher resistivity and better carrier transport property.
High quality CdZnTe epitaxial thick films with thickness of about 1.1 mm were grown on GaAs (001) substrates by close spaced sublimation method (CSS). The dislocation density of the CdZnTe epitaxial films were found to be approximately 1.05 × 10⁵ cm⁻², and the full width at half maximum intensity of X-ray rocking curve is 166 arcsec. The mobility-lifetime (μτ) product and mobility (μ) of electrons were measured to be 1.0 × 10⁻³ cm²V⁻¹ and 750 cm² V⁻¹s⁻¹, respectively. The CdZnTe thick film detector has an energy resolution of 2.2% for ²⁴¹[email protected] MeV alpha particles and 31% for ²⁴¹[email protected] KeV gamma-ray.
Preventing radioactive sources from being used for harmful purposes is a global challenge. A requirement for solving the challenge is developing radiation detectors that are efficient, sensitive, and practical. Room temperature semiconductor detectors (RTSDs) are an important class of gamma-ray sensors because they can generate high-resolution gamma-ray spectra at ambient operating temperatures. A number of diverse and stringent requirements must be met for semiconducting materials to serve as sensors in RTSD spectrometers, which limits the number of candidates of interest that receive attention and undergo focused research and development efforts. Despite this, the development of new compounds for sensors in RTSDs is a thriving research field, and a number of materials with stunning potential as RTSD materials have emerged within the last decade. In this perspective, the state of the art in RTSD materials is examined, and emerging semiconducting compounds are reviewed. The highly developed CdTe, CdZnTe, HgI2, and TlBr are first discussed to highlight the potential that can emerge from RTSD compounds in advanced stages of technological development. Thereafter, emerging compounds are reviewed by class from chalcogenides, iodides and chalcohalides, and organic-inorganic hybrid compounds. This work provides both a compilation of the physical and electronic properties of the emerging RTSD candidates and a perspective on the importance of material properties for the future of compounds that can transform the field of radiation detection science.
