An Analytical Model of the Frequency Dependent 3-D Current Spreading in Forward Biased Shallow Rectangular p-n Junctions

Recently, we presented an analytical model of the frequency-dependent spreading of the small-signal minority carrier flow in forward biased shallow p-n junctions, having stripe and circular geometries and an ohmic bottom contact. This paper extends this approach to model a practical rectangular junction, which could be eccentric, have rounded corners and have an HI-LO junction characterized by a finite surface recombination velocity at the bottom. The current spreading is expressed in terms of the junction length and width, lateral and vertical extent beyond the junction, diffusion length, lifetime, surface recombination velocity, and frequency. It is shown that the spreading in a circular junction approximates that in a square junction of the same area, and the spreading in the direction of a side, which is more than four times the diffusion length can be neglected. The model is validated using TCAD simulation.