Surface and implantation effects on p-n junctions

The contribution of the graded region of implanted p-n junctions is analysed using an exponential profile. Though previously neglected, the authors have recently shown that this contribution to the saturation current of HgCdTe diodes is significant. Assuming a dominant Auger recombination, an analytical solution to the continuity equation is obtained. An expression for the current generated by the graded region is presented for both ohmic and reflecting boundary conditions. A revised condition for a 'wide' region is derived. When the region is 'narrow', the current differs drastically from that of the zero-gradient case. The effects of the junction depth and the substrate and surface concentrations on the current are investigated. It is shown that the reverse current does not saturate.