Position sensitive hybrid pixel detectors have been fabricated by bump bonding silicon or bulk grown semi-insulating gallium arsenide pixel detectors to CMOS read-out chips. Their performance as X-ray Imaging sensors, in the energy range of 10-70 keV, was evaluated in terms of spatial resolution. For the GaAs device a fit was made to the line spread function (LSF) obtained from the image of a narrow slit and the corresponding modulation transfer function (MTF) and noise equivalent passband (N-e) evaluated. A value of 5.7 line pairs per mm (lp/mm) was found for the latter, with a modulation of 10% at the Nyquist frequency (N-y). A comparison is also given of the performance of these devices with state-of-the-art scintillator on silicon CCD dental X-ray sensors. In a bid to improve detector performance, thick layers of high quality GaAs have recently been grown by low pressure vapour phase epitaxy (LP-VPE). Hall measurements on initial samples gave free carrier concentration of 1-8 x 10(11) cm(-3). From the C-V dependence of a reverse-biased Schottky diode this material, however, a space charge density of 2 x 10(13) cm(-3) was measured. The observed temperature and frequency dependency of the capacitance is characteristic of the presence of deep levels and so the material is believed to have a small degree of compensation due to these levels. The measured charge collection efficiency determined (c.c.e) for 60 keV gamma rays showed an increase with reverse bias, reaching a plateau value of 93% for 100V. The limitations of present detectors are discussed and possible future developments indicated.
|Title of host publication||IEEE Transactions on Nuclear Science: proceedings of the 44th IEEE Nuclear Science Symposium and Medical Imaging Conference|
|Place of Publication||New York|
|Number of pages||7|
|Publication status||Published - 1998|
|Event||1997 IEEE Nuclear Science Symposium and Medical Imaging Conference - Albuquerque, United States|
Duration: 9 Nov 1997 → 15 Nov 1997
|Conference||1997 IEEE Nuclear Science Symposium and Medical Imaging Conference|
|Period||9/11/97 → 15/11/97|
- pixel detectors
- x-ray imaging
Bates, R., Campbell, M., Da Via, C., Heijne, E., Heuken, M., Jurgensen, H., Ludwig, J., Manolopoulos, S., Marder, D., Mathieson, K., O'Shea, V., Raine, C., Rogalla, M., & Smith, KM. (1998). Developments in GaAs pixel detectors for X-ray imaging. In O. Nalcioglu (Ed.), IEEE Transactions on Nuclear Science: proceedings of the 44th IEEE Nuclear Science Symposium and Medical Imaging Conference (Vol. 1&2, pp. 534-540). IEEE.