Development of AlGaAs avalanche diodes for soft X-ray photon counting

We report on the performance of avalanche photodiodes (APDs) based on the wide band gap material AlGaAs which have been developed for soft X-ray spectroscopy applications. A number of diode types with different layer thicknesses have been characterised. The temperature dependence of the avalanche multiplication process at soft X-ray energies in Al 0.8 Ga 0.2 As APDs was investigated at temperatures from +80°C to -20°C. X-ray spectra from a 55 Fe radioactive source show these diodes can be used for spectroscopy with promising energy resolution (0.9-2.5keV) over a wide temperature range. The temperature dependence of the pure electron initiated multiplication factor (M e ) and the mixed carrier initiated avalanche multiplication factor (M mix ) were experimentally measured. The experimental results are compared with a spectroscopic Monte Carlo model for Al 0.8 Ga 0.2 As diodes from which the temperature dependence of the pure hole initiated multiplication factor (M h ) is determined.