The spectral resolution of high temperature GaAs photon counting soft X-ray photodiodes

Circular mesa GaAs p+–i–n+ diodes for photon counting soft X-ray spectroscopy have been fabricated and characterised over a temperature range of +80 to –30 °C. The spectroscopic performance of the diodes, as measured by the FWHM of the Mn Kα X-ray line from an 55Fe radioisotope, is reported. In addition, we compare the GaAs diodes with previously fabricated and characterised Al0.8Ga0.2As p+–i–n+ diodes of similar geometry.