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.
Highlights
Wide bandgap materials, such as GaAs,1–5 SiC,6–8 diamond,9,10 Al0.52In0.48P,11–13 and AlxGa1–xAs,14–16 are of interest for use in space science and extreme terrestrial applications where detectors are exposed to high temperatures and intense radiation
Traditional Si X-ray spectrometers often require significant shielding and cooling mechanisms in order to function within extreme environments (e.g., )20 C), whereas wide bandgap detectors are more robust and can possess superior energy resolution at high temperatures due to lower thermally induced leakage currents
The benefits exhibited by AlxGa1–xAs have led to the extensive study of Al0.8Ga0.2As for X-ray detection, where 200 lm diameter Al0.8Ga0.2As circular mesa pþ-i-nþ photodiodes with 1 lm i layers were characterised as soft Xray photon counting detectors, with an energy resolution (FWHM) of 1.07 keV at 5.9 keV at room temperature for the best performing diode
Summary
Wide bandgap materials, such as GaAs, SiC, diamond, Al0.52In0.48P,11–13 and AlxGa1–xAs, are of interest for use in space science and extreme terrestrial applications where detectors are exposed to high temperatures and intense radiation. Traditional Si X-ray spectrometers often require significant shielding and cooling mechanisms in order to function within extreme environments (e.g., ) C), whereas wide bandgap detectors are more robust and can possess superior energy resolution at high temperatures due to lower thermally induced leakage currents.. The benefits exhibited by AlxGa1–xAs have led to the extensive study of Al0.8Ga0.2As (i.e., higher Al composition than the present devices) for X-ray detection, where 200 lm diameter Al0.8Ga0.2As circular mesa pþ-i-nþ photodiodes with 1 lm i layers were characterised as soft Xray photon counting detectors, with an energy resolution (FWHM) of 1.07 keV at 5.9 keV at room temperature for the best performing diode.. The devices were grown and fabricated to the Authors’ specifications at the EPSRC National Centre for III-V Technologies, Sheffield, UK
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