Temperature dependence of Al0.2Ga0.8As X-ray photodiodes for X-ray spectroscopy

Two custom-made Al0.2Ga0.8As p(+)-i-n(+) mesa X-ray photodiodes (200 mu m diameter, 3 mu m i layer) have been electrically characterised across the temperature range 20 degrees C to 60 degrees C. The devices were connected to a custom-made charge sensitive preamplifier to produce an AlGaAs photoncounting X-ray spectrometer. The devices' responses to illumination with soft X-rays from an Fe-55 radioisotope X-ray source (Mn K alpha = 5.9 keV; Mn K beta = 6.49 keV) were investigated across the temperature range 20 degrees C to 20 degrees C. The best energy resolution (FWHM at 5.9 keV) achieved at 20 degrees C was 1.06 keV (with the detector at 10V reverse bias). Improved FWHM was observed with the devices at temperatures of 0 degrees C (0.86 keV) and 20 degrees C (0.83 keV) with the photodiode reverse biased at 30 V. The average electron hole pair creation energy was experimentally measured and determined to be 4.43 eV +/- 0.09 eV at 20 degrees C, 4.44 eV +/- 0.10 eV at 0 degrees C, and 4.56 eV +/- 0.10 eV at 20 degrees C. Published by AIP Publishing.