Articles you may be interested inHigh dynamic range active pixel sensor arrays for digital x-ray imaging using a -Si : H J. Vac. Sci. Technol. A 24, 850 (2006); 10.1116/1.2192526 X-ray detection by direct modulation of an optical probe beam-Radsensor: Progress on development for imaging applications Rev. Sci. Instrum. 75, 3995 (2004); 10.1063/1.1790055High resolution x-ray spectroscopy using GaAs arrays Because the rate of indirect photon-electron conversion for scintillator materials coupled with arrays of photodiodes is at least 25 times smaller than the rate of direct conversion, we examine the conditions to be fulfilled by semiconductors undergoing such direct conversion to be applied to x-ray imaging. Bulk grown materials are not well suited to this application, because large defect concentrations give rise to strongly nonuniform electronic properties. We argue that only epitaxial layers are suitable for use as imaging devices and we illustrate our argument using the case of thick epitaxial GaAs layers. Detectors made with such layers exhibit a good energy resolution, a charge collection efficiency which approaches 1, linearity over more than three orders of amplitude, no afterglow (a response time shorter than 20 µs), and no charge-induced polarization effects.
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