International
Tables for
Crystallography
Volume C
Mathematical, physical and chemical tables
Edited by E. Prince

International Tables for Crystallography (2006). Vol. C, ch. 7.1, pp. 629-630

Section 7.1.6.3.1. X-ray-sensitive semiconductor PSD's

U. W. Arndtb

7.1.6.3.1. X-ray-sensitive semiconductor PSD's

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For X-ray diffraction applications, the main disadvantage of semiconductor devices is that the universal trend in their manufacture is in the direction of miniaturization, leading to a very small pixel size. Thus, imaging devices with up to 2000 × 2000 pixels have been produced but the pixel size is typically ∼10 µm for CCD's and ∼20 µm for PDA's; in most X-ray diffraction applications, it would be difficult to scale down sample and source sizes to a point where the pattern size is appropriate to a semiconductor imager, even though a 2000 × 2000 CCD with 27 × 27 µm pixels is available.

Semiconductor point counters cooled to 80 K are characterized by their very high energy resolution (better than 2% in the 8 keV region). Some counting PSD's potentially have a similar energy resolution. Two-dimensional X-ray-sensitive CCD's for X-ray astronomy research have been used as photon counters (Walton, Stern, Catura & Culhane, 1985[link]; Lumb, Chowanietz & Wells, 1985[link]) but they can only be used at very low counting rates. In integrating devices, the energy discrimination is lost. Silicon detectors for visible-light applications are made with depletion depths of the order of 10 µm. For the detection of 8 keV photons with more than 90% efficiency, depletion depths of 165 µm are necessary and these can be produced only from very high resistivity material (Howes & Morgan, 1979[link]). Moreover, in commercial visible-light imagers, the depletion region is covered by circuitry or by an inactive layer that constitutes an absorbing window for X-ray detection. For the detection of X-rays or electrons, it is, therefore, customary to thin the device and to illuminate it from the back (see, for example, Meyer-Ilse, Wilhelm & Guttmann, 1993[link]).

One-dimensional X-ray detectors utilizing PDA's, such as those made by the Reticon Corporation, have found a number of applications, especially in dispersive X-ray absorption spectroscopy (EXAFS) (Jucha, Bonin, Dartyge, Flank, Fontaine & Raoux, 1984[link]).

A particular problem with silicon detectors is the damage caused by the incidence of X-rays or of energetic electrons. The effects can be minimized by masking all but the active part of their device and by operating it at low temperatures (Jucha et al., 1984[link]).

The use of the room-temperature semiconductor mercuric iodide in place of silicon seems promising (Patt, Delduca, Dolin & Ortale, 1986[link]).

The X-ray diffraction applications of directly sensitive semi-conductor PSD's are likely to remain limited. A previous conversion to visible light or to electrons offers the possibility of an optical or electron-optical demagnification onto the imager, as well as of avoiding some of the other problems discussed above (Deckman & Gruner, 1986[link]).

References

Deckman, H. W. & Gruner, S. M. (1986). Formal alterations in CCD-based electro-optic X-ray detectors. Nucl. Instrum. Methods, A246, 527–533.
Howes, M. J. & Morgan, D. V. (1979). Editors. Charge-coupled devices and systems. New York: John Wiley.
Jucha, A., Bonin, D., Dartyge, E., Flank, A. M., Fontaine, A. & Raoux, D. (1984). Photodiode array for position-sensitive detection using high X-ray flux provided by synchrotron radiation. Nucl. Instrum. Methods, 226, 40–45.
Lumb, D. H., Chowanietz, E. G. & Wells, A. A. (1985). X-ray imaging with GEC/EEV CCD's. IEE Conf. Publ. (London), 253, Suppl.
Meyer-Ilse, W., Wilhelm, T. & Guttmann, P. (1993). Thinned back-illuminated CCD for X-ray microscopy. Proc. SPIE, 1900, 241–245.
Patt, B. E., Delduca, A., Dolin, R. & Ortale, C. (1986). Mercuric iodide X-ray camera. IEEE Trans. Nucl. Sci. NS-33, 523–526.
Walton, D., Stern, R. A., Catura, R. C. & Culhane, J. L. (1985). Deep-depletion CCD's for X-ray astronomy. SPIE Proc. 501.








































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