Effective recombination velocity at the NN+ interface

The effective recombination velocity S_nn⁺ at the nn⁺ interface in buried layer (nn⁺p) and n epi-n⁺ substrate structures has been studied using a model which takes into account the retarding outdiffusion region, recombination and bandgap narrowing. The variation of S_nn⁺ with diffusion length and bandgap narrowing has been estimated taking into consideration their doping-dependence. An attempt has been made to explain the wide range in the reported values for S_nn⁺ using the results of this study.Results indicate clearly the difference between the S_nn⁺ of the two structures. This difference arises from the collection by the p-substrate which accounts for a significant part of the S_nn⁺ of the buried layer structure over a wide range of values of diffusion length. This collection component of S_nn⁺ is sensitive to bandgap narrowing.On the other hand, the S_nn⁺ of the nn⁺ structure is largely determined by the recombination in the outdiffusion region which is sensitive mainly to the value of diffusion length in that region. The component of S_nn⁺ representing recombination in the n⁺ substrate is sensitive to bandgap narrowing. The present study indicates the dependence of S_nn⁺ on the structure and processing of the devices in which the nn⁺ interface occurs.