InGaP (GaInP) mesa p-i-n photodiodes for X-ray photon counting spectroscopy

In this paper, for the first time an InGaP (GaInP) photon counting X-ray photodiode has been developed and shown to be suitable for photon counting X-ray spectroscopy when coupled to a low-noise charge-sensitive preamplifier. The characterisation of two randomly selected 200 μm diameter and two randomly selected 400 μm diameter In 0.5 Ga 0.5 P p + -i-n + mesa photodiodes is reported; the i-layer of the p + -i-n + structure was 5 μm thick. At room temperature, and under illumination from an 55 Fe radioisotope X-ray source, X-ray spectra were accumulated; the best spectrometer energy resolution (FWHM) achieved at 5.9 keV was 900 eV for the 200 μm In 0.5 Ga 0.5 P diameter devices at reverse biases above 5 V. System noise analysis was also carried out and the different noise contributions were computed.