Interpretation of recombination at c-Si/SiNx interfaces by surface damage

Abstract

The measured effective surface recombination velocity Seff at the interface between crystalline p-type silicon (p-Si) and amorphous silicon nitride (SiNx) layers increases with decreasing excess carrier density Δn<1015 cm−3 at dopant densities below 1017 cm−3. If such an interface is incorporated into Si solar cells, it causes their performance to deteriorate under low-injection conditions. With the present knowledge, this effect can neither be experimentally avoided nor fully understood. In this paper, Seff is theoretically reproduced in both p-type and n-type Si at all relevant Δn and all relevant dopant densities. The model incorporates a reduction in the Shockley–Read–Hall lifetime in the Si bulk near the interface, called the surface damage region (SDR). All of the parameters of the model are physically meaningful, and a parametrization is given for numerical device modeling. The model predicts that a ten-fold reduction in the density of defect states within the SDR is sufficient to weaken this undesirable effect to the extent that undiffused surfaces can be incorporated in Si solar cells. This may serve to simplify their fabrication procedures. We further discuss possible causes of the SDR and suggest implications for experiments.