Theoretical study of neutron effects on PIN photodiodes with deep-trap levels

In the present work, the influence of deep-trap levels on the dark current of silicon PIN photodiodes under 1 MeV neutron radiation has been investigated by means of a complete numerical analysis. The computational code used for simulations, developed by the authors, numerically solves the coupled Poisson and continuity equations on a 2D domain to obtain the behavior of electronic devices. Recombination through deep levels in the bandgap is described by the Shockley–Read–Hall (SRH) theory. Defects caused by radiation are quantified in terms of the damage coefficient K for the minority carrier lifetime. The effects of the radiation studied are atomic displacement damages. Results corroborate that the dark current is strongly affected by energy levels close to the midgap. A relationship between the current damage rate and the trap level location in the silicon bandgap was obtained. A model to calculate the dark current of irradiated devices doped with deep impurities is presented. Simulations have allowed the comparison of radiation tolerances of undoped and gold-doped devices. The higher gold density has shown a marked improvement of the hardness of the devices to radiation effects.