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

Abstract

Two custom-made Al0.2Ga0.8As p+-i-n+ mesa X-ray photodiodes (200 μm diameter, 3 μm i layer) have been electrically characterised across the temperature range −20 °C to 60 °C. The devices were connected to a custom-made charge sensitive preamplifier to produce an AlGaAs photon-counting X-ray spectrometer. The devices' responses to illumination with soft X-rays from an 55Fe radioisotope X-ray source (Mn Kα = 5.9 keV; Mn Kβ = 6.49 keV) were investigated across the temperature range −20 °C to 20 °C. The best energy resolution (FWHM at 5.9 keV) achieved at 20 °C was 1.06 keV (with the detector at 10 V reverse bias). Improved FWHM was observed with the devices at temperatures of 0 °C (0.86 keV) and −20 °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 °C, 4.44 eV ± 0.10 eV at 0 °C, and 4.56 eV ± 0.10 eV at −20 °C.

Temperature characterisation of spectroscopic InGaP X-ray photodiodes

“…As is the case for Al0.8Ga0.2As [30,33] and Al0.2Ga0.8As [31], the electron-hole pair creation energy value reported here at 300 K for In0.5Ga0.5P does not lie either on the main or secondary Klein function branches [1,36]. If In0.5Ga0.5P was on the main Klein function branch, the expected εInGaP would be 6.17 eV, which is substantially higher than that found here (4.95 eV ± 0.03 eV).…”

“…If it was on the secondary Klein function branch, the expected εInGaP would be 4.07 eV, which is substantially lower than the obtained value. This lends further weight to the view that the Klein relationship is incomplete [31].…”

“…For the room temperature (20 °C) measurements of the electron-hole pair creation energy, a method similar to that reported by other researchers [28,29,30,31] was used.…”

“…The Fano factor for In0.5Ga0.5P has not yet been measured, but assuming a Fano factor of 0.12 (as for GaAs [37]), the Fano limited energy resolution would be expected to be 139 eV at 5.9 keV at 20 °C. If the Fano factor was 0.099 (as for CdZnTe [38]) a Fano limited energy resolution of 127 eV at [31]. Figure 11 shows the average electron-hole pair creation energy for Ge, Si, GaAs, Al0.2Ga0.8As, Al0.8Ga0.2As, Al0.52In0.48P [39], and In0.5Ga0.5P, and as a function of their respective bandgap energies, at a temperature of 300 K. Figure 11.…”

AlInP photodiode x-ray detectors

“…A c c e p t e d M a n u s c r i p t 7 diameter diode[25], 1.06 keV at 20 °C for a 200 µm diameter photodiode[26]). A shaping time noise analysis is presented in section 3.3.…”