Al0.2Ga0.8As 2 × 2 square pixel X-ray photodiode array

A monolithic 2 × 2 square pixel Al0.2Ga0.8As p+-i-n+ mesa X-ray photodiode array (each photodiode area 200 μm by 200 μm, 3μm i layer) has been fabricated from material grown by MOVPE. The array was electrically characterised across the temperature range 100 °C to -20 °C. Each pixel's response to illumination with soft X-rays from an 55Fe radioisotope X-ray source (Mn Kα=5.9 keV; Mn Kβ=6.49 keV) was investigated across the temperature range 30 °C to -20 °C. The best energy resolution (FWHM at 5.9 keV) achieved at 20 °C was 0.76 keV ± 0.06 keV (with 30 V reverse bias applied to the detector). The measured energy resolution is the best so far reported for AlGaAs X-ray photodiodes at 20 °C. It is also the first time a small AlGaAs X-ray photodiode array has been demonstrated. Due to the temperature tolerance and the radiation hardness of AlGaAs, such detectors are expected to find utility in future space science missions exposed to intense radiation environments, for example missions to study the Jovian or Saturnian aurorae and high temperature planetary surfaces.