Forward voltage drop across a PN junction diode at high current densities †

Abstract

Abstract To calculate the forward voltage drop across a PN junction diode at high current densities, it is necessary to either solve a system of non-linear differential equations by numerical methods for specific cases or to approximate the electric field in the bulk to obtain closed form solutions. Commonly used approximations have small errors as long as the diode is narrow. They fail for diodes of more than a diffusion length thickness. A different, less approximate approach described here yields a closed form solution for this case as well and can also be applied to the narrow diode case. Thick diodes are those diffused in non-epitaxial substrates and are usually made by students in microelectronic laboratories of universities. Analysis is made of a series of such diode structures, having different substrate resistivities, with normalized thickness taken as parameter. The fraction of the external voltage lost on the bulk is calculated for each resistivity-thickness combination and the results summed i...