Some remarks about the use of the charge-neutrality approximationin the simulation of diffusion processes

Doping profiles in bipolar devices are numerically calculated taking into account the actual space charge produced during the diffusion process, which is described by standard models based upon effective diffusivities. The influence of this charge on the diffusion of dopants was examined for arsenic/boron double diffusion in order to evaluate the errors on profiles obtained using the well-known approximation of space-charge neutrality. Numerical results show that this approximation satisfactorily predicts practical doping profiles except for short-time low-temperature diffusion