Synchrotron characterization of deep depletion epitaxial GaAs detectors
Publication date: 16 October 1999
Authors: Owens, A., et al.
Journal: Journal of Applied Physics
Volume: 86
Issue: 8
Page: 4341-4347
Year: 1999
Copyright: American Institute of Physics
We report the results of a series of synchrotron characterizations of two epitaxial GaAs detectors of active areas 2.22 mm² and thicknesses 40 and 400 microns. In spite of an order of magnitude difference in depletion depths, the detectors were found to have comparable performances at ~ -40 °C, with energy resolutions of ~1 keV fwhm at 7 keV rising to ~2 keV fwhm at 200 keV and noise floors in the range 1-1.5 keV. At the lower energies, the energy resolution was dominated by leakage current and electromagnetic pick-up. At the highest energies, however, the measured resolutions appear to approach the expected Fano limit; e.g., ~950 eV at 200 keV. Both detectors were remarkably linear, with average rms non-linearities of 0.2% over the energy range 10-60 keV. By raster scanning the active areas with 20 x 20 micron² monoenergetic photon beams, it was found that the non-uniformity in the spatial response of both detectors was less than 1% and independent of energy. The material used to fabricate the detector is extremely pure. For example, low temperature photoluminescence measurements indicate that the density of the As anti-site defect (EL2) is of the order of 1012 cm-3, which is ~ 2-3 orders of magnitude lower than that generally reported. This indirect measurement of material purity is confirmed by Monte-Carlo simulations of the detector X-ray response, which show that in order to reproduce the observed energy-loss spectra, electron and hole trapping cross-section/density products must be <<1 cm-1.
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