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

AbstractThree custom-made Al0.2Ga0.8As p-i-n mesa X-ray photodiodes (200µm diameter, 3µm i layer) were electrically characterised and investigated for their response to illumination with soft X-rays from an 55Fe radioisotope X-ray source (Mn Kα = 5.9keV; Mn Kβ = 6.49keV). The AlGaAs photodiodes were shown to be suitable for photon counting X-ray spectroscopy at room temperature. When coupled to a custom-made low-noise charge-sensitive preamplifier, a mean energy resolution (as quantified by the full width at half maximum of the 5.9keV photopeak) of 1.24keV was measured at room temperature. Parameters such as the depletion width (1.92µm at 10V), charge trapping noise (61.7 e−rms ENC at 5V, negligible at 10V) and the electronic noise components (known dielectric noise (63.4 e− rms), series white noise (27.7 e−rms), parallel white noise (9.5 e−rms) and 1/f series noise (2.2 e−rms) at 10V reverse bias) affecting the achieved energy resolution were computed. The estimated charge trapping noise and mean energy resolution were compared to similar materials (e.g. Al0.8Ga0.2As) previously reported, and discussed. These results are the first demonstration of photon counting X-ray spectroscopy with Al0.2Ga0.8As reported to date