Energy response characterization of InGaP X-ray detectors

Two custom-made In0.5Ga0.5P p(+)-i-n(+) circular mesa spectroscopic X-ray photodiodes with different diameters (200 mu m and 400 mu m) and a 5 mu m i layer have been characterized for their response to X-ray photons within the energy range 4.95 keV to 21.17 keV. The photodiodes, operating uncooled at 30 degrees C, were coupled, in turn, to the same custom-made charge-sensitive preamplifier. X-ray fluorescence spectra of high-purity calibration foils excited by a Mo target X-ray tube were accumulated. The energy resolution (Full Width at Half Maximum) increased from 0.79 +/- 0.02 keV at 4.95 keV to 0.83 +/- 0.02 keV at 21.17 keV, and from 1.12 +/- 0.02 keV at 4.95 keV to 1.15 +/- 0.02 keV at 21.17 keV, when using the 200 mu m and 400 mu m diameter devices, respectively. Energy resolution broadening with increasing energy was attributed to increasing Fano noise (negligible incomplete charge collection noise was suggested); for the first time, the Fano factor for In0.5Ga0.5P was experimentally determined to be 0.13, suggesting a Fano limited energy resolution of 145 eV at 5.9 keV. The charge output of each system had a linear relationship with photon energy, across the investigated energy range. The count rate of both spectroscopic systems increased linearly with varying X-ray tube current up to similar to 10(5) photons s(-1) cm(-2) incident photon fluences. The development of In0.5Ga0.5P based spectrometers is particularly important for hard X/gamma-ray astronomy, due to the material's large linear X-ray and gamma-ray absorption coefficients and the ability to operate uncooled at high temperatures. Published by AIP Publishing.