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_0.8Ga_0.2As APDs was investigated at temperatures from +80°C to -20°C. X-ray spectra from a ⁵⁵Fe 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_0.8Ga_0.2As diodes from which the temperature dependence of the pure hole initiated multiplication factor (M_h) is determined.