First spectroscopic X-ray and beta results from a 400 µm diameter Al0.8Ga0.2As photodiode

Results characterising the performance of thin (1 µm active layer) 400 µm diameter Al0.8Ga0.2As mesa photodiodes operated at room temperature are presented showing the spectral response under illumination with moderate energy X-rays (5.9 keV and 22.16 keV) from radioisotope X-ray sources (55Fe and 109Cd) and beta particles from a 14C source (endpoint energy = 156.48 keV). The X-ray FWHM is established as 1.95 keV at 5.9 keV and 22.16 keV, primarily limited by electronics noise from the preamplifier. The diodes show a spectral response to 14C beta particles, but the endpoint energy is not reached due to the detector's thinness. The X-ray results are compared with 200 µm diameter Al0.8Ga0.2As photodiodes previously characterised using X-ray radioisotope sources at our laboratory.