Temperature characterisation of spectroscopic InGaP X-ray photodiodes

In this paper for the first time, an InGaP photodiode was used in a high temperature tolerant X-ray spectrometer. The use of InGaP in X-ray spectrometers shows a significant advance within this field allowing operation up to 100 degrees C. Such results are particularly important since GaP and InP (the InGaP binary parent compounds) are not spectroscopic even at room temperature. The best energy resolution (smallest FWHM) at 5.9 keV for the InGaP spectrometer was 1.27 keV at 100 degrees C and 770 eV at 20 degrees C, when the detector was reverse biased at 5 V. The observed FWHM were higher than the expected statistically limited energy resolutions indicating that other sources of noise contributed to the FWHM broadening. The spectrometer's Si preamplifier electronics was the limiting factor for the FWHM rather than the InGaP photodiode itself. The InGaP electron-hole pair creation energy (epsilon(InGaP)) was experimentally measured across the temperature range 100 degrees C to 20 degrees C. epsilon(InGaP) was 4.94 eV +/- 0.06 eV at 20 degrees C.