Abstract
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.
Original language | English |
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Title of host publication | IEEE Transactions on Nuclear Science: proceedings of the 44th IEEE Nuclear Science Symposium and Medical Imaging Conference |
Editors | O Nalcioglu |
Place of Publication | New York |
Publisher | IEEE |
Pages | 534-540 |
Number of pages | 7 |
Volume | 1&2 |
ISBN (Print) | 0780342593 |
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
Conference | 1997 IEEE Nuclear Science Symposium and Medical Imaging Conference |
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Country/Territory | United States |
City | Albuquerque |
Period | 9/11/97 → 15/11/97 |
Keywords
- GaAs
- pixel detectors
- x-ray imaging
- photonics
- instrumentation