Statistical modeling of radiation-induced proton transport in silicon: deactivation of dopant acceptors in bipolar devices

We show that radiation-induced dopant deactivation in MOS capacitors that simulate the base oxides of silicon bipolar transistors is due primarily to direct neutralization by protons. The strong dependence of the deactivation process on electric field is related to the transport of H⁺ in the depletion region. The probability of acceptor neutralization near the Si surface is higher for small irradiation biases when protons diffuse through the depletion layer rather than drift through it. The observed dependence of the neutralized-acceptor concentration on the irradiation bias is explained by analytical modeling and statistical Monte Carlo simulations. The analytically estimated and numerically calculated density of passivated acceptors near the Si-SiO₂ interface is in very good agreement with experimental data. Neutralization of protons in the Si is not necessary to describe the observed dopant deactivation.