Abstract
We report on hard X-ray measurements with two epitaxial GaAs detectors of active areas 2.22mm2 and thicknesses 40 and 400μm at the ESRF and HASYLAB synchrotron research facilities. The detectors were fabricated using high-purity material and in spite of an order of magnitude difference in depletion depths, they were found to have comparable performances with energy resolutions at −45°C of ∼1keV fwhm at 7keV rising to ∼2keV fwhm at 200keV and noise floors in the range 1–1.5keV. At energies <30keV, the energy resolution was dominated by leakage current and electromagnetic pick-up, while at the highest energies measured, the resolutions approach the expected Fano limit (e.g., ∼1keV near 200keV). Both detectors are remarkably linear, with average rms non-linearities of 0.2% over the energy range 10–60keV, which, taken in conjunction with Monte-Carlo results indicate that charge collection efficiencies must be in excess of 98%. This is consistent with material science metrology which show that the material used to produce them is of extremely high purity with impurity concentration <1013cm−3.
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