Diffusion in ideal cylindrical and spherical junctions—Apparent diffusion length

Unless junction depths are scaled in the same ratio as other device dimensions, the trend toward smaller devices leads to a relative enhancement of junction-edge effects. In this work, we present some analytical formulas describing the injection of current in ideal step-junction diodes having either plane, cylindrical, or spherical geometries. A normalized surface-recombination velocity S^*is used to characterize the adjacent boundary condition. Both blocking and collecting contacts may be modeled by a choice of S^*.