A prototype 200 μm diameter Al0.52In0.48P p+-i-n+ mesa photodiode (2 μm i-layer) was characterised at temperatures from 100 °C to −20 °C for the development of a temperature tolerant photon counting X-ray spectrometer. At each temperature, X-ray spectra were accumulated with the AlInP detector reverse biased at 0 V, 5 V, 10 V, and 15 V and using different shaping times. The detector was illuminated by an 55Fe radioisotope X-ray source. The best energy resolution, as quantified by the full width at half maximum (FWHM) at 5.9 keV, was observed at 15 V for all the temperatures studied; at 100 °C, a FWHM of 1.57 keV was achieved, and this value improved to 770 eV FWHM at −20 °C. System noise analysis was also carried out, and the different noise contributions were computed as functions of temperature. The results are the first demonstration of AlInP's suitability for photon counting X-ray spectroscopy at temperatures other than ≈20 °C.
The room temperature X-ray responses as functions of time of two n type cubic GaN Schottky diodes (200 μm and 400 μm diameters) are reported. The current densities as functions of time for both diodes showed fast turn-on transients and increases in current density when illuminated with X-ray photons of energy up to 35 keV. The diodes were also electrically characterized: capacitance, implied depletion width and dark current measurements as functions of applied bias at room temperature are presented. At −5 V reverse bias, the capacitances of the diodes were measured to be (84.05 ± 0.01) pF and (121.67 ± 0.02) pF, respectively. At −5 V reverse bias, the dark current densities of the diodes were measured to be (347.2 ± 0.4) mA cm−2 and (189.0 ± 0.2) mA cm−2, respectively. The Schottky barrier heights of the devices (0.52 ± 0.07) eV and (0.63 ± 0.09) eV, respectively, were extracted from the forward dark current characteristics.
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